Wikipedia:Reference desk/Archives/Science/2010 July 19

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July 19

corn fields

why is corn very small and scarce around the edges of corn fields?--Horseluv10 00:09, 19 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

Huh? Do you mean in areas where it was not intentionally planted, or where the fertilizer missed?? Edison (talk) 02:11, 19 July 2010 (UTC)

The use of fertilizer is sometimes by purpose lower at the edge to meet the law that a undisturbed rim has to grow around the fields.--Stone (talk) 04:58, 19 July 2010 (UTC)

i mean where it is intentionally planted.--Horseluv10 12:04, 19 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

You can think of lots of reasons - that the farmer didn't fertilize the edges of the field as well as the center because of the need to turn the tractor around...or maybe there are trees around the edges of the field that are sucking up the ground water...or if the field is irrigated, that the irrigation system doesn't extend all the way to the edges...or maybe that insecticides aren't being sprayed out to the edges (again, for the tractor-turning-around reason). Perhaps the plants in the center of the field are better shielded from the wind than the ones that only have neighbors on one side. It's hard to know which of those things it might be. I couldn't find any online information about such a phenomena. SteveBaker (talk) 14:54, 19 July 2010 (UTC)

The phenomenon is observed in this paper, but sadly it's behind a paywall so I can read anything but the abstract. The Google description says "For all crops, crop height was significantly greater in the field centre than in the sprayed edges", although the paper refers to pesticides and herbicides rather than fertiliser. SteveBaker's ideas sound good though. Brammers (talk/c) 15:45, 19 July 2010 (UTC)

Outlying plants are exposed more than sheltered plants to wind and possibly competition from other plant roots underground. Cuddlyable3 (talk) 22:51, 19 July 2010 (UTC)

I was also thinking that if some kind of flying pest arrived at random in or around the field, all of the plants in the center of the field would have about an equal chance of getting infested - but if a pest arrived just outside the boundary of the field, it would presumably make its way to the plants at the outer edge. That would make any given plant at the edge of the field much more likely to get pest infestations than one in the main part of the field.

Also, some plants exude chemicals that supress plants from other species from growing nearby - and again, this would benefit the plants in the center of the field to a greater extent than the ones at the edge because the combined contributions of greater numbers of plants would build up a higher concentration of the chemical. SteveBaker (talk) 22:57, 19 July 2010 (UTC)

Not to mention that "edges of corn fields" that us non-farmers are likely to see are the edges that face roads. Many plants are not happy growing immediately next to a road. APL (talk) 15:45, 20 July 2010 (UTC)

solar cells, photovoltaic, photosynthesis

I'd like some boffins to create a (short) entry that answers;

1. What are the best solar cells (for electricity) (then for heating). 1a. Explain why UV solar cells aren't worth producing. Doesn't the higher energy of UV make up for the lower frequency range (compared to visible light) [implied NOT in Solar Cell entry] 1b. Explain why IR solar cells aren't worth producing. Doesn't the much greater frequency range make up for the lower energy (compared to visible light) [also implied NOT in Solar Cell entry]

2. Why aren't countries - especially Japan and Australia - investing more in solar cell research than in oil exploration - when Australia has so much sun - and Japan is so dependent on oil, and so strong in technical stuff

3. Why can't plant photosynthesis be mimicked in an artificial photosynthesis, to produce a 100% efficient solar cell.

PS I hope the shift apostrophe is the "tilde"

````MGoold —Preceding unsigned comment added by 220.253.195.35 (talk) 02:27, 19 July 2010 (UTC)

No, the tilde is in the upper left corner of my keyboard. It shows a key with ` and ~ in it. Shift that key and it should work. or click the signature with pen button on the top of the edit window. --Chemicalinterest (talk) 11:01, 19 July 2010 (UTC)

This looks a bit homeworky but anyway on "Why aren't countries investing more in solar cell research than in oil exploration" obvious reasons include (1) because you cannot be granted "concessions" for research into areas of intellectual property whereas you can for oil fields (2) because oil exists and technology to improve solar cells may not exist (3) because of these reasons the rates of return on investment are lower in solar technology than in oil exploration. --BozMo talk 11:34, 19 July 2010 (UTC)

1: Best changes all the time, and by application, so just take a look at the solar cell article and this this image. For heating don't use any solar cell, use solar thermal.

1a, 1b: There isn't enough energy to make it worthwhile. The way it works is this: The higher the frequency you work with the more energy you gain from each photon - but this also means that all photons below the frequency are ignored, so you have less photons. If instead you use a lower frequency, you gain energy from more photons, but each photon gives you less energy, and the rest of the energy is wasted as heat. So there is a perfect frequency where multiplying energy*number of photons is maximized. (I could not immediately find what that number is for the sun.) There is also a Multijunction solar cell which layers the cells, each layer collects from a different frequency. But it's too expensive to be practical except is specialized applications.

2: I can't answer about countries, but solar cells are hard. We've been researching them for something like 40 years. There is another problem: Solar cells cost too much, and it's not just cost - there simply isn't enough rare earth elements on this earth for everyone to switch to solar cells. Unless someone comes up with a technology that uses more common elements solar cells will never be widespread for bulk power. Every time solar cells come out people make an estimate: Once oil goes up in price this much these cells will be cost effective, then you look at a graph of oil prices, predict when that will happen, and declare a date. But one thing is forgotten: When the price of oil goes up, the price of everything goes up right along with it - energy is the prime component of everything we build. If energy cost goes up the price of everything goes up - including those solar cells. So they never actually pass oil, they constantly stay tantalizingly just out of reach. Personally I do not favor photovoltaics for energy. I favor solar thermal. That we can build, and we can build it cheap. It's just not very exciting.

3: Why do you think plants are 100% efficient? They are not. According to the article on it (yes we have one) Photosynthetic efficiency is 11%. But anyway, why bother mimicking it?

Ariel. (talk) 11:35, 19 July 2010 (UTC)

In response to your second point, the prices have been declining for solar PV. A US government study found a decrease of an average 3.5% per year from 1998 to 2007. Mostly in non-panel costs[1]. Also solar PV replaces electricity, not oil unless you are one of the few using your panels to charge your electric car. Very little oil is used to produce electricity (except in a few island nations). Mostly it is a mix of coal, hydro, nuclear, and natural gas. Worldwide only about 6% of electricity is generated from oil but in the US and France for examples it is only around 2%[2] Rmhermen (talk) 16:50, 19 July 2010 (UTC)

Plasma weapon

Would a plasma weapon be feasible? --138.110.206.101 (talk) 03:01, 19 July 2010 (UTC)

Now or the future? =) --mboverload@ 03:21, 19 July 2010 (UTC)

In the future, but specifically handheld plasma weapons. It's obvious that vehicle-mounted plasma weapons will probably be developed somewhat soon. --138.110.206.101 (talk) 03:25, 19 July 2010 (UTC)

Do you mean a weapon that shoots a jet of plasma? That seems pretty impractical to me. The air would cool the jet very fast, limiting its range to less than ten feet. I don't think they will ever build one. --The High Fin Sperm Whale 04:51, 19 July 2010 (UTC)

Maybe the OP is thinking of some sort of Pulsed Energy Projectile as mentioned in Plasma weapon, like [3] [4]? Of course funding is no definative indication of success, it may turn out to be another Gay bomb Nil Einne (talk) 04:56, 19 July 2010 (UTC)

Do you have a source for it being "obvious" that "vehicle-mounted plasma weapons will probably be developed somewhat soon"? Vimescarrot (talk) 10:45, 19 July 2010 (UTC)

They wouldn't have the size constraints of handheld weapons. --138.110.206.101 (talk) 12:51, 19 July 2010 (UTC)

The laws of physics are the same at both sizes. If one is possible, then so is the other, it's just an engineering problem. I suspect neither is possible. What would prevent the jet of plasma from rapidly spreading out and cooling down? --Tango (talk) 13:49, 19 July 2010 (UTC)

Shoot it fast enough that it hits the target before spreading out too much. --138.110.206.101 (talk) 13:53, 19 July 2010 (UTC)

I don't think it works that way. I think it will spread out at roughly the same angle regardless of the speed. --Tango (talk) 15:14, 19 July 2010 (UTC)

The flamethrower has largely been replaced by the shoulder-mounted rocket-launcher as a heavy infantry weapon. The rocket is considered more accurate, more effective, more humane, safer to operate, and suitable in a wider array of tactical conditions, including anti-personnel, anti-vehicle, and anti-bunker. It seems unlikely that a plasma weapon serve a significantly different tactical role than a flame-thrower, except that it would be harder to construct, more complicated, more expensive, and more susceptible to environmental conditions. As such, I would not bet money that any plasma-weapons are going to be in use in the near future. Most plasma physics research is more related to the effects of nuclear weapon detonation; occasionally, by bureaucratic accident, some of that plasma-physics budget trickles into a tactical research group; but that doesn't mean that there is either a practical use or a real need to develop such weapons. Nimur (talk) 16:32, 19 July 2010 (UTC)

It depends alot on what you mean by plasma weapon, according to our plasma weapon article, a plasma weapon is any device that uses plasma as a weapon so there are many different devices that could fall under the catagory of plasma weapon. The pulsed energy projectile uses a laser that ablates part of the targets creating a burst of plasma strong enough to knock a person over or even kill them. This is currently being tested by the military. However, for a device that shoots out a beam of plasma like a flame thrower, the plasma woul most likely disipate and cool to quickly to cause damage.--74.67.89.61 (talk) 23:53, 19 July 2010 (UTC)

If you could somehow encapsulate a bolt of plasma in a magnetic field, you could potentially prevent the two biggest problems facing the use of ionized plasma as a weapon, namely blooming (The dissipation of a plasma when it interacts with other particles like air) and the cooling it would undergo, though I'm not sure such a targeted magnetic field is currently possible, so hypothetically plasma could only be used as a sort of flamethrower as the poster above mentions until such advancements are made. However, plasma could still be used with impunity in a hard vacuum like space, where there would be no blooming effect and cooling would happen at a slower rate as a sort of mid-range heavy assault weapon. —Preceding unsigned comment added by 174.88.50.154 (talk) 04:09, 20 July 2010 (UTC)

Would plasma cause electrocution in addition to burns?

--138.110.206.101 (talk) 03:06, 19 July 2010 (UTC)

At those conditions, I am not sure there'd be much of a distinction. --Jayron32 03:27, 19 July 2010 (UTC)

Plasma are locally neutral, so there wouldn't be any significant voltage differences over your body. But even a cold plasma could give a chemical-like burn via the free ions. --Tardis (talk) 04:09, 19 July 2010 (UTC)

A chemical burn? Not necessarily. Top layer of our skin -- stratum corneum -- is dead, and low-energy ions are extremely unlikely to penetrate it without being neutralized. --Dr Dima (talk) 05:35, 19 July 2010 (UTC)

The phrase "cold plasma" does not mean "plasma at room temperature". It is a measure of the average electron energy. It can only exist in vacuum conditions, or else recombination will neutralize the plasma. Bittencourt has a chapter on the cold plasma model: "This simple model encompasses only the equations of conservation of mass and of momentum." It says nothing about the thermodynamic temperature, nor the effects of sticking your hand into it. Again, for these cold-plasma considerations to be valid, it is almost always a requirement that the density are very low; e.g. such that the thermal velocities are much smaller than the electromagnetic wave speed (not the speed of light - the speed of the plasma oscillation). This is easier to accomplish by changing ionization rates and pressures than by changing the gas temperature. To address the original question: plasmas are often created by conditions (like highly ionizing incident electromagnetic radiation, and a sparse gas) that would be harmful to humans. With or without the ionization, those conditions would be harmful anyway. Direct effects attributable to the plasma would be enhanced chemical reactivity with the free radicals and ions. Everything else - the electromagnetic radiation, the temperature, the pressure, and so on - would be just as harmful as if there were no ionization present. Nimur (talk) 16:43, 19 July 2010 (UTC)

Silver + Phosphate

I've noticed that Wikipedia has no article on Silver phosphate. This leads me to wonder, does this compound exist? And if not, what reaction (if any) would be expected if a solution of Silver ion (like Silver nitrate) was mixed with a solution of Phosphate ion (like Sodium phosphate)? Would any insoluble products be formed? 67.172.250.173 (talk) 04:10, 19 July 2010 (UTC)

Most silver compounds (with the notable exception of the nitrate) are insoluble, so its likely that silver phosphate would be insoluble. If you have access to even a basic high school chemistry laboratory, they are usually stocked with both of those chemicals, so you could ask a teacher to do the experiment yourself. Silver phosphate undoubtedly exists, however not everything that exists merits a Wikipedia aticle. A compound that exists, but which has no practical applications would likely not merit one. --Jayron32 04:34, 19 July 2010 (UTC)

I would think that it is needed. I read in a science kit that one way to test for the aqueous phosphate ion would be to add silver ion, which would precipitate yellow silver phosphate. --Chemicalinterest (talk) 10:55, 19 July 2010 (UTC)

Created it (with redirects); feel free to expand with reliable sources. --Chemicalinterest (talk) 11:30, 19 July 2010 (UTC)

As it turns out Silver phosphate is notable due to its use in photography and analytical chemistry. It also seems to be a topic of current research too.77.86.59.77 (talk) 16:13, 19 July 2010 (UTC)

To answer the question - yes Silver phosphate is formed.77.86.59.77 (talk) 16:13, 19 July 2010 (UTC)

You can find details on the production of silver phosphate in this recently published paper - it's not free, but if you create an account, register an email address and use Special:EmailUser/Smartse, I can email you a copy. I've nominated the article to be in the "did you know" section on the main page, you can find the nomination here Smartse (talk) 14:30, 20 July 2010 (UTC)

Minimum air pressure for sound

What's the minimum air pressure required to carry sound at a detectable volume? Since outer space isn't a complete vacuum, would it be theoretically possible to create a microphone sensitive enough to pick up sound in space? NeonMerlin 04:54, 19 July 2010 (UTC)

That's a very good question. Sound is a pressure and density wave. My first guess would be therefore that for the sound wave to propagate, you need the mean free path of the air molecule, with respect to collisions with other air molecules, to be much shorter than the sound-wave wavelength. The mean free path increases as density decreases, so the longer is the sound wavelength the lower is the lowest air density at which it would still propagate adequately. So I think the wavelength (that is, the frequency) may be more important than the sound volume. Of course, the higher is the sound volume at the source the farther is the distance at which the sound is still detectable; that is also true. --Dr Dima (talk) 05:26, 19 July 2010 (UTC)

According to our Interstellar_space article there are only "a few hydrogen atoms per cubic meter". Far too little for a physical wave to transfer between this. However, this fascinating article has more information - it looks like they have detected "sound" in space, but nothing you would ever be able to hear. You'll need to read it to understand [5] --mboverload@ 05:32, 19 July 2010 (UTC)

More than mean free distance, you'd also need there to be enough collisions between particles to propagate the sound over noise level. As particles spread out, the signal-to-noise ratio grows significantly worse until no meaningful information can be propagated via sound waves. --Jayron32 05:44, 19 July 2010 (UTC)

Not quite what you asked, but density wave theory is relevant. It explains the formation and evolution of galactic spiral arms as a kind of sound wave propagating around the galaxy. The wave leads to episodes of local compression of the interstellar medium, which in turn triggers star formation and gives the appearance of concentrations of bright stars near and immediately after the compression maxima. This explains why the stars in these spiral bands don't actually move at the same apparent velocity as the spiral arms themselves, i.e. the individual stars in the arm that we observe today are only the current generation of stars created by a deeper process propagating through the interstellar medium. In this case the wavelength of the "sound" would be ~10-100 thousand light years. As Dima suggested above, if you make the wavelength long enough even the dilute medium of interstellar space can carry it. Of course, at this scale it isn't "sound" in any sense that humans would be able to directly measure or listen to. Dragons flight (talk) 07:04, 19 July 2010 (UTC)

So you're saying that in space, someone can hear you scream, if you scream at a low enough pitch and the other person's eardrums are really really big? --Trovatore (talk) 07:06, 19 July 2010 (UTC)

Pretty much, yes. Really big larynx and really, really big eardrums :) --Dr Dima (talk) 08:58, 19 July 2010 (UTC)

An analogy would be trying to transmit the details of a picture by a few bytes of information; the information is not enough to get the details. --Chemicalinterest (talk) 11:05, 19 July 2010 (UTC)

The commonly used "zero" reference sound pressure in air is 20 µPa RMS, which is usually considered the threshold of human hearing (at 1 kHz). Cuddlyable3 (talk) 13:59, 19 July 2010 (UTC)

And since we were talking about plasmas above, here: magneto-acoustic waves. Plasmas, being electrically conductive and therefore responsive to electromagnetic effects, can sustain acoustic longitudinal compression waves at much lower density, because ions can "collide" (interact electromagnetically) at greater distance than a neutral atom (which must only interact electrostatically). Naturally, there is a difference between ordinary sound waves and these effects; and it would be hard to put a regular acoustic transducer microphone to pick up the pressure fronts; but these are definitely compression waves at much lower gas density than ordinary sound. They are observed experimentally, usually by deducing the effective gas density from electromagnetic/radio signatures, and exist in the earth's magnetosphere, on the sun, and in the solar wind. Nimur (talk) 16:53, 19 July 2010 (UTC)

I should respond to Mboverload's linked article, as well as to responses to Dragons Flight. The linked article talks about sound (or intermolecular interaction) propagating in a very dense, relative to "empty space", cloud around a black hole. This sound wave emitted X-rays which are just ordinary light, and those are what we detected on Earth. So no, no sound went through normal 10-atoms-per-m^3 space, and in space no one will hear you scream ever because those molecules will not interact with each other on anything near that energy scale ever. Even the density waves Dragons talks about that generate spiral arms involve actual net motion of massive amounts of matter on the wavelength scale, which is very different from sound we hear every day in which matter actually moves net forward on a scale much much smaller than wavelength. SamuelRiv (talk) 08:22, 20 July 2010 (UTC)

Maps for streams

Where can I get maps for streams? I know Microsoft MapPoint, Google Maps, and Bing Maps do not like copying. Is there any other place to get maps? --Chemicalinterest (talk) 11:51, 19 July 2010 (UTC)

"...do not like copying." Copying to what end? Maps are basically always intended for use as maps; it's not a problem to print one off and use it as such. On the other hand, copying to resell is going to be breaking the copyright of virtually any map provider, not just online ones. Can you more clearly describe your purpose? — Lomn 12:25, 19 July 2010 (UTC)

The US government has lots of maps that are free (worldwide maps, not just US). Here are a few sites: [6] [7] [8] [9]. Ariel. (talk) 12:38, 19 July 2010 (UTC)

Articles for streams, such as the Shallow Brook and all other ones, are greatly enhanced by a map. I wanted to know where I could get maps for streams from. --Chemicalinterest (talk) 12:40, 19 July 2010 (UTC)

There might be something listed here which might help. --Tagishsimon (talk) 13:32, 19 July 2010 (UTC)

OpenStreetMap allows you to choose what data to export. Warofdreams talk 15:29, 19 July 2010 (UTC)

The other editors at WikiProject Rivers may have more ideas. Rmhermen (talk) 16:22, 19 July 2010 (UTC)

Used Seamless Maps on USGS. Resolved. --Chemicalinterest (talk) 23:04, 19 July 2010 (UTC)

Catnip and REM sleep

Is there a relationship between catnip exposure and increased REM sleep time in cats? Also, can anyone speculate as to what cats dream about? My cat refuses to respond to my questions but insists on being scratched behind the ears. Viriditas (talk) 12:07, 19 July 2010 (UTC)

I can't provide a source, but I do recall seeing a program on TV in Australia some time back in which a cat appeared to stalk prey while asleep. ("Asleep" as determined by measuring brainwave activity.) Presumably the cat was dreaming about stalking prey. Mitch Ames (talk) 13:46, 19 July 2010 (UTC)

I don't know about cats - but dogs certainly dream and I'm as sure as it's reasonably possible to be that they are dreaming of chasing and hunting and such. Dogs seem less able than humans to shut off the connection between brain and muscles when dreaming (Atony). Some people who suffer from Rapid eye movement behavior disorder have the same problem. In dogs, you can see their feet making small movements that start out sequenced alternately like they are walking, then switch to front-feet-together/back-feet-together like they are running. You can see their breathing speed up - sometimes you can hear tiny little barks. Then, suddenly you might see their jaws making little movements - one of my dogs would salivate at this point in the dream. It's hard to believe we aren't watching the dog dream of walking around in the park, seeing a squirrel, chasing it and probably catching and maybe eating it. If cats suffer the same lack of atonia that dogs do, then carefully watching your cat sleep might well give you some kind of insight as to what's going on in their furry little brains. SteveBaker (talk) 14:41, 19 July 2010 (UTC)

In my experience, cats do not engage in the same kind of thing, or at least don't do it as regularly. I've owned cats all my life and have only seen the occasional twitch or two - nothing like the drama Steve mentions above. Perhaps there's some kind of tie in to hunting styles; dogs chase down their prey, so it makes sense they dream about running. Perhaps my cat is dreaming intently about lying in ambush and I'm mistaken in thinking it's sleeping like a log (in much the same way my math teacher misinterpreted my attempts at afternoon meditation). Matt Deres (talk) 17:29, 19 July 2010 (UTC)

Yes, exactly. My experience is that cats just don't have REM as much as dogs. However, after leaving approximately 1 gram of dried, ground, organic catnip for my cat to play with every day for a month, I noticed that he began to have REM every day in the late evening, and I've never seen a cat do it that much, leading me to conclude that the catnip was influencing his dream state. His legs move as if he's running and jumping, his whiskers twitch like he's poking his face through a bush, etc. That's why I'm asking. Viriditas (talk) 18:27, 19 July 2010 (UTC)

Well, if you're going to dose your pet to the eyeballs with a strong (for a cat) hallucinogenic drug...you're bound to get some odd side-effects! What's strange about this is that in humans, the active ingredient in catnip is a mild sedative and an antispasmodic - which I'd naively imagine would help to dampen down atonia rather than enhance it...but then cats aren't humans...so all bets are off. SteveBaker (talk) 22:49, 19 July 2010 (UTC)

The cat "hunting" during REM sleep probably had surgery on locus coeruleus similar to experiments by Michel Jouvet #Cat dreams --Digrpat (talk) 18:24, 19 July 2010 (UTC)

Apparently the main active ingredient in catnip, nepetalactone, or its metabolic byproduct nepetalic acid, is a mild sedative and hallucinogen. However I haven't been able to spot any studies that discuss its neural mechanism of action, so I don't think it is possible to say anything about its effects on REM sleep. Looie496 (talk) 23:23, 19 July 2010 (UTC)

Alcubierre drive

Would an Alcubierre drive require large quantities of some sort of chemical compound (like the dilithium used in Star Trek's warp drives)? --138.110.206.101 (talk) 12:52, 19 July 2010 (UTC)

Our article on Alcubierre drives certainly seems to suggest so. Physchim62 (talk) 13:08, 19 July 2010 (UTC)

I meant, is there a single specific substance would be required in large quantities, which would play a role in the future similar to dilithium in Star Trek? --138.110.206.101 (talk) 13:12, 19 July 2010 (UTC)

Since this drive does not exist, there is no way to answer this. Ariel. (talk) 14:57, 19 July 2010 (UTC)

The article indicates it would require exotic matter. That's probably a good candidate for "dilithium" as anything else. --Mr.98 (talk) 15:32, 19 July 2010 (UTC)

Indeed, although I would guess (and guessing is all we can really do) that if exotic matter is possible then it would need to be made synthetically, rather than mined. --Tango (talk) 21:57, 19 July 2010 (UTC)

Scientific name of Clown Dorid

Hi, I am attempting to find the scientific name of the Clown Dorid so that I can make a mention of the Clown Dorid name in the appropriate wikipedia article, or make a new article if this animal doesn't have a page already. I found this picture which is described as a Clown Dorid in Victoria, B.C., Canada. At wikipedia, the closest picture I can find is the Triopha catalinae (sea clown Triopha). But the pictures don't look exactly the same, and I kind of doubt it is the same animal. Can you help me figure this out? Thanks. Fallendarling (talk) 14:22, 19 July 2010 (UTC)

According to this page, the Clown Dorid is Triopha catalinae. I think the 'sea clown' is the same thing - and the differences in those photos you link to are not significant. SteveBaker (talk) 22:35, 19 July 2010 (UTC)

scratching: survival benefits

Background:

The instinct to scratch is very strong and spreads through all of the mammal and apparently into at least some fish. Conventional medical advice is always that you must not scratch. However, behavior which is very widely distributed in the animal kingdom normally has some survival benefit. I am surprised to find no postings on the survival benefit of scratching.

With skin parasites such as tics and fleas, I can see that scratching would be a benefit, in that it has a real chance of physically eliminating the parasite. I would also suggest that scratching can help with mosquito bites and poison ivy etc., because causing the lymph and blood to leak from the skin would help purge locally concentrated toxins.

Searching the web shows lots of references to scratching being an indication of parasite infection but does not suggest that scratching helps it. I found nothing on the concept of eliminating locally concentrated toxins, as I mention above.

Question:

Can anybody give some informed comment on this?

Perhaps this could be a topic for a post-graduate biology student. Fixer Anderson (talk) 14:32, 19 July 2010 (UTC)

The usual theory, as you say, is that the reflex to scratch is intended to remove insects. Scratching at other times is probably just the body making a mistake. Evolution doesn't result in optimal solutions, just "good enough" solutions. The harm from scratching when you don't have an insect on you is minimal, so the evolutionary pressure to develop more refined itch sensations is very small. --Tango (talk) 15:51, 19 July 2010 (UTC)

Yup, I'd go with "mistake" because other situations produce same/similar sensation to the presumed evolutionarily-good trigger. If it's really conserved mechanistically across species, then it's gotta be something low-level like a reflex arc or something else that doesn't require substantial advanced sensing or processing (i.e., easy to trigger false-positive). But still, seems easy to co-opt existing sensory input (a certain level/location/size of touch?)...not sure what more specific sign one could have that didn't require substantially more/more-advanced sensing. DMacks (talk) 17:17, 19 July 2010 (UTC)

Did anyone else get itchy reading this question? Googlemeister (talk) 19:13, 19 July 2010 (UTC)

I'm pretty sure the general understanding is that scratching serves to remove irritants of every sort from the skin, including contaminants, skin damaged by sunburn, etc. If you Google around for "pruritis" (the medical term for itching), you should be able to get some leads into the literature. Looie496 (talk) 19:31, 19 July 2010 (UTC)

It's actually spelled pruritus, which might help with the Googling. It's not the -itis ending meaning "inflammation", but some different etymology. I think it's pronounced PROOR-it-us but I'm not sure of that.

Similarly for tinnitus (ringing in the ear), which again I think is pronounced TINN-it-us. --Trovatore (talk) 18:51, 21 July 2010 (UTC)

Dragons using chemicals to generate fire?

It seems to have become a trend now to describe fantasy dragons that use chemical compounds to create flames--as in the movie Reign Of Fire. Supposedly "if a beetle can do it a dragon can too", except that the bombardier beetle doesn't create sparks/flames, just boiling liquid. Are there really chemical mixtures an animal could use to create a flame, or is the whole concept just bunk? 75.200.39.63 (talk) 16:31, 19 July 2010 (UTC)

Sure. We have evidence that at least one animal can learn to use chemicals to produce fire. See also, fossil record of fire. Lots of chemical mixtures will work, so long as the mixture completes the fire triangle. I would think that any other animals that wanted to create flame would have to use similar approaches - naturally-occurring materials, like wood, sulfur, and phosphates, plus air, plus an ignition source. Nimur (talk) 16:58, 19 July 2010 (UTC)

see http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2010_May_22#Is_there_any_animal_that_can_.27emit.27_fire.3F

There are many chemical mixtures that catch fire when mixted eg potassium permanganate/glycerin - do animals produce such mixtures, or the components is sufficiently concentrated form - no. It's bunk.

The oft mentioned Bombardier beetle produces hydrogen peroxide at only 10% [10] that's nothing like enough to produce a fire .. if the concentration was high enough the beetle would have burned its ass off thousands of years ago in a spontaneous beetle combustion evolutionary dead end !

But real D&D Dragons aren't made of organic matter - so that doesn't matter.. 77.86.59.77 (talk) 17:06, 19 July 2010 (UTC)

Living organisms can produce hydrogen and methane, both of which are flammable - a mixture that is known to combust is flatus, as many videos on Youtube will testify. No doubt a bit of fantasy digestive tract re-plumbing could occur to make a fire-breathing dragon. Brammers (talk/c) 17:51, 19 July 2010 (UTC)

And an animal with the worst case of bad breath in the entire animal kingdom! SteveBaker (talk) 22:29, 19 July 2010 (UTC)

You'd still need an ignition system. After all, human fire breathers can blow dragon-like flames with an external source of ignition (and fuel, but the fuel is relatively easy from a biological point of view). Natural selection hasn't delivered us with fire-breathing dragons, probably because it's easier to use the required energy simply to grow bigger and/or cleverer. Physchim62 (talk) 22:41, 19 July 2010 (UTC)

In Anne McCaffrey's fantasy books the dragons produce phosphine which spontaneously ignites in air. I believe there are bacteria that can make this gas. Graeme Bartlett (talk) 02:46, 20 July 2010 (UTC)

Also because the advantage is not at all obvious, when compared to the downsides. Consider that soldiers only use flamethrowers in very specific situations—they are not very "general" weapons, unless you want to set your house on fire on a regular basis. --Mr.98 (talk) 18:58, 20 July 2010 (UTC)

Von Kossa Stain

Von Kossa Stain on the web makes no sense eg [11] the calcium is reduced by the strong light and replaced with silver deposits

The wikipedia article (here before I edited it) seems to make more sense - it says it is a test for bone phosphate. What's going on?77.86.59.77 (talk) 16:47, 19 July 2010 (UTC)

Is your question about calcium vs phosphate? Does this help? Ariel. (talk) 02:46, 20 July 2010 (UTC)

Yes - I was just trying to come to terms with the wrongness of many apparently reliable looking sources that clearly state it is an agent for calcium.87.102.13.208 (talk) 02:59, 20 July 2010 (UTC)

Info about the changing face of the Earth

It is about the GEOLOGICAL changes, how it is formed and its reasons. eg:1. Formation of mountains,rivers,valleys etc 2. Information about the tectonic plates. Please check about it in WIKEPEDIA or any other information giving websites188.135.2.50 (talk) 17:16, 19 July 2010 (UTC)

It appears that you copied a homework question here. We will not do your homework. The answers you seek are in the articles on Wikipedia. See mountain, river, and valley. You will also want erosion. The second question brings up tectonic plates. -- kainaw™ 18:42, 19 July 2010 (UTC)

And orogeny - learn the meaning of this word and impress your teacher! Personally, I've always been interested in comparative orogeny on extraterrestrial worlds, as it provides one of the best scientific justifications for planetary explanation of solid-surface planets and moons. It's very strange that mountains and valleys can develop on worlds that do not have seismic or tectonic activity, nor water or air to erode them. But, mountains and valleys do exist up there.... Nimur (talk) 23:41, 19 July 2010 (UTC)

Don't forget lakes too. Smartse (talk) 13:55, 20 July 2010 (UTC)

Teeth

Hello Why is it that teeth do not attempt to repair themselves? Surely in primitave man, broken damaged teeth would have been a threat to survival. This seems the only part of the body without the will to try and heal. Thanks Ossiee (talk) 17:21, 19 July 2010 (UTC)

We discussed a related question last April. The real issue is not so much why they don't repair themselves, as to why we only have two sets of teeth, rather than having a continuously replenishing number. Primates can't do this, but rodents can, but they sacrifice having teeth that fit well together, which humans kind of rely on. Keep in mind that this is not an evolutionary question limited to primitive man—this is a trait that evolved more generally with primates and probably even earlier than that. --Mr.98 (talk) 17:33, 19 July 2010 (UTC)

It's all part of the Grand Scheme by the Great Dentist in the Sky, looking after his chosen ones. Clarityfiend (talk) 22:33, 19 July 2010 (UTC)

We have this article: Hyperdontia. Bus stop (talk) 22:38, 19 July 2010 (UTC)

We grow one extra set of molars in our 20s, so primitive man had a few back-up teeth. 142.104.215.130 (talk) 22:47, 19 July 2010 (UTC)

Your premise is false -- teeth do not only attempt to but often succeed in repairing themselves. Sclerotic dentin is that dentin that has been exposed to noxious stimuli and has hardened in an attempt to block further insult (usually bacterial enzymatic toxins) and root canals become increasingly calcified when similarly exposed to bacterial insult. The fact that teeth cannot regenerate -- well, that is something entirely different. The majority of the human body cannot regenerate. Lost fingers, toes, eyes, ears, genitourinary structures, digestive tract structures, etc. are gone forever. It is only the very rare case that chordate organisms can completely regenerate lost limbs and or other minor body parts, such as amphibians, which can grow back appendages and then the famous (even) human liver that can regenerate. Peripheral nerves can also grow back, but my point is that teeth are far from the exception, so your query seems a bit misguided. DRosenbach <sup>(Talk | Contribs)</sup> 02:50, 20 July 2010 (UTC)

Indeed. My husband has a full set of perfect teeth because his filled teeth grew back and pushed the fillings out: he also has never lost a tooth. (It's nice to know it is a recognised medical phenomenon!) --TammyMoet (talk) 08:11, 20 July 2010 (UTC)

Dental repair only occurs on a level that it is barely-to-somewhat macroscopically recognizable -- chunks of missing tooth structure will not grow back, because that would be regeneration, not repair. The latter is resolution of bodily destruction with foreign or different tissue types, while the former is resolution with identical tissue types, perfectly restoring the wound or site of tissue destruction to its pre-damaged state. DRosenbach <sup>(Talk | Contribs)</sup> 17:49, 20 July 2010 (UTC)

Most mammals are diphyodonts, with two successive sets of teeth. However, there are at least two exceptions. Both elephants and manatees are polyphyodonts, with multiple replacement sets of molars - according to our article, an elephant has five or sometimes six sets of molars in its lifetime. Note that these are complete replacement teeth - this is different from rodents, whose incisors grow continually but are not replaced if lost. Gandalf61 (talk) 11:01, 20 July 2010 (UTC)

My grandmother had a third set of teeth and my own extra randomly-placed teeth were surgically removed when I was a young child. See super-numerary teeth. (which I now see is a redirect to the earlier mentioned Hyperdontia.) Rmhermen (talk) 18:07, 20 July 2010 (UTC)

How does your comment relate to the OP's question? DRosenbach <sup>(Talk | Contribs)</sup> 02:24, 21 July 2010 (UTC)

In the past, primitive man had a short life for all sorts of other reasons. It's only with modern medicine that man survives long enough for tooth loss to become a problem, and since modern dentistry makes sure this is not fatal, there is still no evolutionary pressure for such an adaption. Evolution only does enough to ensure survival to reproductive age-anything else is a luxury only to be changed (hopefully) with genetic engineering or regenerative medicine.[Trevor Loughlin]80.1.88.12 (talk) 13:11, 23 July 2010 (UTC)

Dextropropoxyphene

On the graph shown, where exactly does, the drug dextropropoxyphene stand. I, precisely, mean the red & grey capsule in the centre.

Thanks  Jon Ascton  (talk) 18:37, 19 July 2010 (UTC)

Probably mid way on the Y axis and pretty low on the X axis (depending on dose). As an opioid derivative it's going to be pretty addictive (at least in the long term) but, given it's wide availability as a drug to treat (and not to abuse), it's going to be fairly low on the physical harm side. Regards, --—Cyclonenim | Chat  19:07, 19 July 2010 (UTC)

That graph was put together by an expert following lots of research. We aren't experts and don't have the time or resources to do lots of research, so we can't work out where any other drugs would appear on that graph. --Tango (talk) 19:25, 19 July 2010 (UTC)

And in any case, as has been discussed here a few times, it's unclear how literally one should take that particular graph, as it doesn't account for the fact that numerous drugs come in different forms that have different propensities for harm and addictiveness (e.g. the difference between chewing coca leaf or smoking crack cocaine, both of which are technically the same drug). --Mr.98 (talk) 19:39, 19 July 2010 (UTC)

We can't work out exactly where a drug can go on that graph, but we can speculate based on it's properties that we do know. If a drug is an opiate, it's going to have a high risk of dependency. Regards, --—Cyclonenim | Chat  19:41, 19 July 2010 (UTC)

Note that the harm figure is an average of acute, chronic and injected harm - mostly chronic harm roughly mirrors dependance (with expceptions), also this means that drugs that are not injected score 2/3 of other similarly 'harmful drugs'. 178.78.65.223 (talk) 19:53, 19 July 2010 (UTC)

I mentioned this earlier. I object to using average as a measure of harm on this graph. I think they should have used max. Ariel. (talk) 21:23, 19 July 2010 (UTC)

The problem with using the maximum known harm is that one person could have reacted badly to a drug due to all sorts of reasons, even genetic defects. If a random drug kills one person because of a defect, but causes only mild harm in the others, do you use the maximum harm? Of course not. That's why you have to use averages. Regards, --—Cyclonenim | Chat  21:48, 19 July 2010 (UTC)

I don't mean maximum harm among various people, I mean maximum from the three types of harm listed in the accompanying table: Acute, Chronic, Intravenous Ariel. (talk) 22:14, 19 July 2010 (UTC)

Oh, sorry, completely misunderstood! I agree, e.g. Heroin should definitely have a harm of 2.8 if that's the acute harm value given but the rest are lower. Regards, --—Cyclonenim | Chat  23:40, 20 July 2010 (UTC)

Scrotal implosion

what is Scrotal implosion and why is it trending on twitter? —Preceding unsigned comment added by 86.159.8.157 (talk) 18:44, 19 July 2010 (UTC)

It's just nonsense hoping to become a meme. 178.78.65.223 (talk) 19:12, 19 July 2010 (UTC)

Check out http://www.whatthetrend.com/. It gives explanations of what all the things that are trending are and why they are trending. --Tango (talk) 19:21, 19 July 2010 (UTC)

Apparently, this one is a joke medication side effect from a recent episode of The Boondocks. --Tango (talk) 19:22, 19 July 2010 (UTC)

you can see the source here http://www.youtube.com/watch?v=vMvKIHw7bCI 178.78.65.223 (talk) 19:28, 19 July 2010 (UTC)

Two dimensional thrust vectoring

If you took an aircraft, such as the F-22, and remove the vertical stabilizers to make it more Stealthy, and replace them with yaw-controlling thrust vectoring nozzles, yet still maintain the agility of the fighter? I know of the X-36, but the article didn't say much about its performance. --The High Fin Sperm Whale 19:24, 19 July 2010 (UTC)

The article x-36 says The X-36 possessed high maneuverability that would be ideal for use as a fighter. I see no reason why not. 178.78.65.223 (talk) 19:37, 19 July 2010 (UTC)

There some more info here on the side effects of not having a 'rudder' - notably lack of or reduced yaw stabilty [12] 178.78.65.223 (talk) 19:40, 19 July 2010 (UTC)

See also Tailless aircraft 178.78.65.223 (talk) 19:45, 19 July 2010 (UTC)

The article on tailless aircraft is not much help. It is mostly about aircraft lacking horizontal stabilizers. AS for the first comment, I don't see how I could have missed that! Thanks anyways. --The High Fin Sperm Whale 20:32, 19 July 2010 (UTC)

At the expense of providing an unhelpful answer, "anything can be designed with any parameters you want." More importantly, if you made such a design, would the tradeoff involved be worth the effort? Removing a stabilizer can be done on any aircraft - the result is obviously a less stable aircraft. It will cost more money to design an active control system than a passive one with the same control characteristics and specs. You can look at the specs for a thrust-vectoring system to determine the force, velocity, and time-constant regimes that it can operate over - but I strongly suspect that complete removal of such a major, critical part of the stability and control system of the aircraft would render the airframe virtually uncontrollable. In fact, the advent of the vertical stabilizer is often credited as one of the crucial technologies that made the first heavier-than-air flight possible. Who would have thought that the most important "wing" on the aircraft was the one that didn't provide any lift! The Wright brothers' flyer is more a feat of control than of propulsion, lightweight materials, or any other characteristic - the majority of their innovation was that they could actually steer because they had rudders and wing-warping control. Since control is such an important part of design, it is heavily studied in the design of an airframe. MDATCOM is an aerodynamics program used to design these sorts of things and test them numerically before building models and running them through the wind tunnels. As you begin removing "pieces" from the airframe, you start approaching a missile-like aircraft; you can usually spin stabilize such airframes, but that would be unmanageable if you intended to put a human inside it. Needless to say, this is definitely an ongoing effort in modern defense research - efforts to replace 100% of our aircraft fleet with unmanned aerial vehicles are under way, because removing the human from the flight control equation results in relaxation of many other design constraints. (E.g., instead of a fighter, you could have a highly-maneuverable, spin-stabilized, steerable cruise missile for all of our air-to-air and air-to-ground combat needs). This would be cheaper to build, could operate more stealthily, could be more fuel-efficient/longer-range; could turn faster (without a pilot, there is virtually no restriction on turning radius, maximum G-force, and so on). Nimur (talk) 20:55, 19 July 2010 (UTC)

Also keep in mind that an aircraft which relies on thrust vectoring to control yaw requires thrust, so there would be no control without thrust. This situation could occur after engine failure, and would occur on every flight when the throttles are at idle during approach and landing. anonymous6494 21:54, 19 July 2010 (UTC)

For this reason, spacecraft (including the Space Shuttle orbiter, which is not very aerodynamic, despite its superficial "airplane" shape) have a primary propulsion system and a separate reaction control system. An RCS is easier to build and is more reliable than a vectored thrust nozzle; and it can be designed to provide 6-degree-of-freedom maneuverability. Nimur (talk) 23:44, 19 July 2010 (UTC)

Huh? The space shuttle can't use its primary propulsion after the external tank drops away. The RCS does orbital manuevers, but only orbital manuevers. Once it reaches aerodynamic altitudes on descent, the shuttle uses control surfaces like a plane. Rmhermen (talk) 05:01, 20 July 2010 (UTC)

I beg to differ - the Orbital Maneuvering System does orbital, and only orbital, maneuvering. But the RCS, a separate propulsion system on STS, is also used during descent for orientation and velocity control. Space Shuttle also has control surfaces, including a rudder and ailerons; but RCS is useful because it can provide independent, 6-DOF attitude and translation. See this NASA science brief: STS Reaction Control System: descent maneuvering is "...accomplished by using either control stick steering commands or automatic commands as inputs to the equations. The solution of these equations results in fire commands to the available RCS jets and/or appropriate orbiter aerosurfaces." Loosely speaking, STS has three different types of propulsion: primary propulsion (comprising the ET and SRBs, and the Space Shuttle Main Engine); the OMS (comprising the "jet pods" on the "tail"; and the RCS, comprising all the other small nozzles tucked neatly away throughout the rest of the Orbiter. Nimur (talk) 07:55, 20 July 2010 (UTC)

You are correct on the only-orbital part. From our article: "The aerodynamic shape is a compromise between the demands of radically different speeds and air pressures during re-entry, subsonic atmospheric flight, and hypersonic flight. As a result the orbiter has a high sink rate at low altitudes, and transitions from using RCS thrusters in low pressure to flight surfaces at low altitudes." That low altitude is minimum 45,000 feet when the last of the RCS shuts-off (the first part shuts-off at whatever altitude "dynamic pressure of 10 lbs/sq foot" corresponds to). However I can't find any point that the main engine and the RCS are functional at the same time. Flight control on ascent is managed with main engine gimbals, not the RCS or shuttle flight surfaces. Flight control on descent is managed by RCS until each flight surface becomes useful in thickening atmosphere. Flight control in space is handled by OMS and RCS but is non-aerodynamic. So the example fails to illustrate. Rmhermen (talk) 18:02, 20 July 2010 (UTC)

reply to anonymous6494 -- an interesting point. That means the plane would behave quite like a jetski - maneuverable only when powered. A very counter-intuitive situation for most people, especially when approaching a dangerous obstruction. 218.25.32.210 (talk) 07:44, 20 July 2010 (UTC)

Bates method

Are here any Bates method users? (I have read Wikipedia:Reference_desk/Guidelines/Medical_advice and I am not seeking medical advice). 83.31.74.163 (talk) 21:30, 19 July 2010 (UTC)

Currently? I'm sure some people are still trying it - but you are aware that studies have shown conclusively that it doesn't work...right? SteveBaker (talk) 22:23, 19 July 2010 (UTC)

It certainly has its fans. Its crazy, irrational, fans. If a popular blog makes a post about glasses or LASIK, there's a reasonable chance someone who's never posted a comment on that blog before will show up and post a diatribe about it. If you search Instructables you'll find many howtos covering simplified versions of the Bates method. I'm not sure why Instructables doesn't make an effort to remove such nonsense.

Another related bit of crazy is pinhole glasses. (Pin-hole glasses really do work as a primitive replacement for corrective lenses. But they're always sold as a cure-all that will magically fix your eyes. Which is proven to be nonsense.) APL (talk) 23:07, 19 July 2010 (UTC)

Take for example this: [13]. Comments by Andrei and ceanes say that this method is helpful. 83.31.89.30 (talk) 11:14, 20 July 2010 (UTC)

Exactly. You could post an article about any crazy, proven-not-to-work, doesn't-even-make-sense, folk cure you can think of, and you'd get a dozen internet comments from people who swear it works and that there is a global conspiracy to cover it up.

It's all so predictable, really. APL (talk) 14:42, 20 July 2010 (UTC)

What about Huxley? 83.31.96.69 (talk) 19:39, 20 July 2010 (UTC)

He made a lot of money selling books to suckers. If he did use the Bates method to improve his eyesight that wouldn't tell the rest of us anything useful, Huxley's vision was damaged by keratitis, not by a natural nearsightedness.

However, he didn't improve his visual acuity. From one of the sources in our article :

"It is often pointed out that Huxley's visual acuity has not improved in any extraordinary way. He admits that. The point is that he has learned how to use what he has to better advantage. It is not the primary retinal sensation that is improved; it is. the neglected, but vitally important, cerebral part of seeing that has been trained."

That is to say, it's all in his head and he admits as much. His eyes have not actually improved at all. (As Bates claims!) Huxley is only claiming that he has trained his BRAIN to make better use of his poor eyes.

It's flim-flam. When proponents of some great new technique start telling you that they can improve things, but not in a ways you can measure, then you know you're dealing with flim-flam. It's tough to tell if people like that are honestly self-deluded or if they're just scam artists, but either way you're better off steering clear. APL (talk) 19:59, 20 July 2010 (UTC)

Can probiotics develop antibiotic resistance?

After watching my toddler endure violent diarrhea resulting from his intestinal flora being completely wiped out by the amoxicillin he had to take for cellulitis, I began to wonder: Is it possible for probiotics to develop antibiotic resistance, so that when you need to take antibiotics, the beneficial organisms that normally live in your intestines won't be harmed?

I'm curious if there have ever been any studies conducted wherein healthy people take deliberately incomplete antibiotic doses, to kill off some of the beneficial bacteria, leaving the remainder to breed stronger. And if so, how long would the effect last? ~Amatulić (talk) 23:01, 19 July 2010 (UTC)

In principle I don't see anything against it. But I have a feeling it would not develop in humans. Harmful bacteria have a strong "motivation" to develop resistance - if they don't they are wiped out. The probiotic ones however, while they might be killed temporarily they will come back (from other people), so they don't really need resistance so badly. I bet it could be done in a lab though - grow cultures with low level doses of antibiotics. But it has a downside: bacteria are able to share genes (Horizontal gene transfer), so if the "good" bacteria had the genes for resistance, it's possible for "bad" ones to copy them. Ariel. (talk) 01:08, 20 July 2010 (UTC)

That seems logical. In that case there wouldn't be a real benefit in developing an antibiotic resistant strain of good bacteria in one's gut. ~Amatulić (talk) 05:09, 20 July 2010 (UTC)

Ariel's explanation does initially seem logical, but I would be very cautious about using the "motivation" argument Ariel proposes since natural selection acts at the level of the individual organism, not at the level of whole populations of bacteria. Consider the following case: a few good bacteria in a person have randomly acquired resistance, either by mutation or by horizontal gene transfer. Antibiotics are then used, which kill all of the sensitive good bacteria, but leave the resistant ones. The resistant ones are the only ones left, multiply and therefore almost all of the good bacteria are now resistant (of course this is simplified - individual antibiotics don't act on all types of bacteria or on all environments within the body). You now have a population of resistant bacteria. It doesn't matter whether or not they are going to be wiped out if they don't develop resistance, the bacteria don't "know" that. If there is a selective pressure and sufficient biological variation resistance will develop. Of course the resistant bacteria would often be less "fit" once the antibiotic is removed (e.g. if they waste energy producing enzymes which break down antibiotics) so may then be replaced by sensitive bacteria acquired from other people, or by a few sensitive bacteria who happened to survive. This sort of fluctuating resistance in "good"/neutral bacteria does actually occur [14] and can be a major problem, since, as Ariel mentions, harmful bacteria can acquire resistance from the good bacteria. This link has more explanation [15]. Equisetum (talk | email | contributions) 09:57, 20 July 2010 (UTC)

In addition, the concept of 'good' bacteria is a little simplistic. For starters, 'good' bacteria could obtain genes which make them pathogenic. More importantly perhaps, even without that in the right circumstances/conditions 'good' bacteria can cause problems. This is somewhat mentioned in the probiotics article although in reference to taking probiotics. In summary, purposely developing antibiotic resistance, even in healthy individuals with a very carefully controlled diet, sounds like a very bad idea. In fact, over prescribing of antibiotics, including to healthy and no so healthy people who won't benefit from them is a concern even when they finish the treatment. This link [16] may be of interest. Nil Einne (talk) 20:56, 20 July 2010 (UTC)

They already do - antibiotic resistance genes are (were) used to make genetically modified plants. Although people still debate the safety of this, the regulators decided that it was safe as the genes were already present in our gut flora (reference 1 reference 2). You might like to read this too - regarding what happens to when you take antibiotics. Smartse (talk) 13:47, 20 July 2010 (UTC)