Wikipedia:Reference desk/Archives/Science/2015 April 21

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April 21

Color of Eggs in Supermarket

The shells of eggs sold in supermarkets here are usually white. But we got some recently that have brown shells. (I'm not suggesting this is a new phenomenon, just that I never thought about it before.)

Looking at a broken shell up close, it is clear that the main material of the shell is white and only the outer surface is brown.

Are the egg manufacturers now staining eggs brown or do some hens create eggs with brown outer surfaces?

And if the latter is true, how on earth do the hens manage to do that?

Thanks, CBHA (talk) 03:50, 21 April 2015 (UTC)

Many types of chickens lay brown eggs. Araucanas even lay blue eggs. This article states "Different breeds of hens just lay different-colored eggs. Quality, flavor, and nutrition aren’t affected." I have some Araucana crosses in my own flock and the colors really throw people off when they first buy the eggs from me. Dismas|^(talk) 04:05, 21 April 2015 (UTC)

I think that natural chicken eggs were originally brown, as camo against would be egg predators. But people thought they looked dirty, especially considering they came out of a chicken's rear, so they were bred to be white. However, there is now a movement back to more natural foods. While the color of the eggshell doesn't necessarily relate to the quality of the contents, people might think that it does. So, those might either be actual brown eggs, or they might have just dyed them brown to trick the consumer. I'm really not aware if the natural pigment on egg shells is just on the surface, but that might make sense, since that's the only place it's needed. StuRat (talk) 04:08, 21 April 2015 (UTC)

Though camouflage may be a factor, the reasons for bird egg colouration being so diverse has been the subject of scientific debate - see here [1] for a few suggestions (incidentally noting the complication that bird colour perception may differ from ours). As for the mechanism, see here [2]: "Shell pigments are secreted by the uterine glands and are chemically related to the bird's blood and bile pigments. Background colors are deposited first during shell formation and secondary markings are deposited on the outer cuticle." AndyTheGrump (talk) 04:21, 21 April 2015 (UTC)

Egg (food)#Color of eggshell has some relevant info. Dragons flight (talk) 04:27, 21 April 2015 (UTC)

An article on egg colour mimicry by the common cuckoo (Cuculus canorus) has more detail on the chemistry of avian eggshell colouration: "avian eggshell colours appear to be predominantly generated by two main pyrrol pigments: biliverdin (responsible for blue–green coloration) and protoporphyrin IX (responsible for brown–red maculation patterns..." [3] For bird species vulnerable to brood parasitism by cuckoos, camouflage may be less important than staying ahead in the evolutionary 'arms race' and laying eggs which can be distinguished from those of the local host-specific cuckoo population. Probably not a factor with the Red junglefowl ancestors of the domestic chicken, but an illustration of just how complex the question may be. AndyTheGrump (talk) 04:40, 21 April 2015 (UTC)

Where are you? This surprises me, I haven't seen white eggs for many years here in the UK. All brown. 82.21.7.184 (talk) 07:04, 21 April 2015 (UTC)

There are various national preferences for eggshell colour, and hens are bred/chosen accordingly. As I understand it, white shells are preferred in the US and brown in the UK. See here for example. AndrewWTaylor (talk) 08:28, 21 April 2015 (UTC)

Germany is pretty mixed. And you get all sizes and all grades (open floor, free range, certified organic - no cage batteries in the EU anymore) in all colours, without, I think, systematically differing perceptions about quality. --Stephan Schulz (talk) 08:59, 21 April 2015 (UTC)

Doesn't the US do other weird stuff to eggs as well? Something with taking the outer layer of the shell off? And insisting the should pointlessly be kept in the fridge etc. 131.251.254.154 (talk) 09:07, 21 April 2015 (UTC)

That's standard procedure in the US, to keep them from rotting so quickly. And the stores refrigerate them too. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:13, 21 April 2015 (UTC)

Yes, it's standard procedure in the USA, but it is aberrant from a world perspective. We only need to refrigerate them because we wash off most of the cuticle. UK/EU eggs are just as safe, and perhaps moreso. They last about as long at room temp as ours do in the fridge. They also require much less energy for processing and shipping. A simple google will give you tons of info [4]. SemanticMantis (talk) 13:35, 21 April 2015 (UTC)

Do those folks also advocate drinking raw milk? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:34, 21 April 2015 (UTC)

Did you read any of the links I googled for you? I like this one [5]. "Those folks" are most of the world, with USA, AU and Japan being the main exceptions. Some of "those folks" surely drink raw milk, but milk at the grocer in the UK and AU is usually pasteurized, which you would know if you looked at Pasteurization or raw milk. As one of the ref desk's most prolific posters, surely you know how to look things up? By comparing to raw milk (which does have some health risks because of how we treat our dairy cows in the USA), you seem to be implying there is something unsafe about eggs in the UK, because they do not scour the cuticle off of eggs, thus obviating the need for refrigeration. Such an implication is seriously incorrect, though I apologize if my inference is mistaken. I'm WP:AGF here and assuming that you genuinely want to know more about the topic, even though your comment does seem a bit trollish. Let me know know if you need more references if you can't find them for yourself. I was wrong about one thing: the USA method roughly doubles the shelf life of eggs, according to the NPR article above. But UK eggs are good for about 21 days, though I wouldn't call that "rotting quickly". SemanticMantis (talk) 15:12, 21 April 2015 (UTC)

As soon as someone argues that the US should do what "the rest of the world" does, I am immediately skeptical. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:16, 21 April 2015 (UTC)

I never said anything of the sort, nor has anyone in this thread at time of my posting. None of the articles I linked, or even the top google hits said anything like that. For clarity, the US/UK split is mostly just an interesting difference. I have not seen any data that suggest that either is more safe or effective than the other. You seemed to be implying that the UK method was unsafe, though you didn't actually clarify if that's what you meant or not. Misrepresenting someone's referenced comments like you just did is posting in bad faith, and makes you look like a troll. Please stop. I'm done here, as I no longer believe that you want to learn about the issue. SemanticMantis (talk) 15:27, 21 April 2015 (UTC)

You said "it is aberrant from a world perspective" and then "'Those folks' are most of the world, with USA, AU and Japan being the main exceptions." The term "abberant" is a holier-than-thou type of comment. It's bashing of "non-conformists." If you're done here, that's just as well. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:32, 21 April 2015 (UTC)

You seriously are to thin-skinned. We in the rest of the world are, of course, much more resilient ;-). --Stephan Schulz (talk) 18:52, 21 April 2015 (UTC)

You're kidding right? When confronted with facts, you start throwing insults around? Yes, the US is the odd one out here, that's all. I guess I missed the mass extinction here in the UK caused by us so stupidly not refrigerating our eggs. Fgf10 (talk) 19:44, 21 April 2015 (UTC)

The insult was the term "aberrant". Feel free to yell at the guy who made that inflammatory comment. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:48, 21 April 2015 (UTC)

And this is why eggs have to be refrigerated in the US. Apparently they vaccinate chickens against salmonella in the UK, and they don't here. That doesn't make UK's approach superior. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:52, 21 April 2015 (UTC)

Not to rile you up more, but a) DF mentioned that vaccination two hours before you just below, and b) vaccination against Salmonella may be a good idea in general, and may well further reduce the risk of food-borne illness, but it's not the reason why eggs in the EU are not refrigerated. It's only one of a number of measures to control for Salmonella, and it's by no means used universally in Europe. As for "aberrant" being insulting, I think you should consult a dictionary and WP:AGF - it's principal meaning is "different from the normal case", without value judgement. --Stephan Schulz (talk) 20:36, 21 April 2015 (UTC)

In addition to that insulting phraseology, he called me a troll. He forfeited his expectation of good faith assumption. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:07, 21 April 2015 (UTC)

Sorry, but neither - as I pointed out above - was the "phraseology" insulting, nor did he call you a troll. There is a reason for WP:AGF - it's not to make individual users feel good, its there because it avoids unnecessary conflicts. In terms of game theory, it avoids an endless tit-for-tat retaliation cycle that starts when one of the "players" misreads a situation. --Stephan Schulz (talk) 23:48, 21 April 2015 (UTC)

FWIW I've kept quite a few eggs unrefrigerated in the U.S.; among other things my hope was that I'd smell or see something 'off' if one were infected, as some people who get food poisoning seem to say they did. Of course, it's easier to smell something odd if the egg is warm. But yeah, vaccinating the chickens sounds like a smart idea. You know what sounds like a smarter idea? Vaccinating the humans. Seriously, I don't understand how we ended up with a vaccine for chickens and not for people... might as well ask how rinderpest was annihilated but measles still runs rampant. Wnt (talk) 23:26, 21 April 2015 (UTC)

Keeping eggs in the fridge has a difference aside from spoiling. The most significant egg-borne pathogen is Salmonella. Depending on the estimate, Salmonella contaminated eggs are responsible for between 40,000 and 150,000 illnesses per year in the US. Salmonella contaminated eggs generally have an identical appearance to uncontaminated eggs. However, the bacteria will proliferate at room temperature but not when refrigerated, meaning that if an egg has been contaminated then it becomes more hazardous to humans if stored at room temperature. As a percentage, relatively few eggs are contaminated, but given how many eggs we consume the absolute numbers are still large. An important difference between the US and other places is that the UK and parts of Europe have adopted comprehensive vaccination of chickens against Salmonella. As a result, the UK has seen their Salmonella illnesses fall from ~15,000 / year to only a few hundred / year. God only knows why, but the US has resisted vaccinating chickens. Cooking and careful handling (e.g. washing hands and surfaces exposed to raw eggs and/or chicken meat) can prevent Salmonella transmission, but refrigeration also remains an important tool for delaying Salmonella growth in the US where it remains a major health concern. Dragons flight (talk) 17:50, 21 April 2015 (UTC)

The prevalence of brown or white eggs in the supermarket depends on consumer preference. Here in the UK, the change of preference from white to brown eggs coincided with a change in preference from white to brown bread - thought to be a consumer belief that brown is healthier than white.__DrChrissy ^(talk) 09:27, 21 April 2015 (UTC)

Yes this is discussed in the article linked by Dragons Flight above. Nil Einne (talk) 13:37, 21 April 2015 (UTC)

In the US, eggs sold in supermarkets are typically white, but I've also see brown eggs as long as I can recall. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:13, 21 April 2015 (UTC)

It depends on the locality. When I grew up in New England, brown eggs were more common and slightly less expensive, so we always had brown eggs at the house. White were available, but less common. Where I live now in North Carolina, the exact opposite situation occurs: the White eggs are more plentiful and less expensive, so those tend to dominate. It just depends on the local chicken situation. In New England, the local farmers have chickens that lay brown eggs. There used to even be a jingle that ran on radios and TVs that extolled the virtues of buying locally produced brown eggs. Of course, assuming all other factors are equal (size, age, storage, etc.) between the two, there is no functional difference between brown eggs and white eggs. --Jayron32 13:36, 21 April 2015 (UTC)

Yeah this is also mentioned in our article linked article. Note also that while the last comment seems to be true for brown and white eggs, it may not be true for some types of blue eggs which may have more durable shells. (No idea what percentage of blue eggs this applies to, as they are not very common it could be a fair percentage.) Although the research was a very long time ago and I have no idea what happened to the crossbreeding attempts. Nil Einne (talk) 16:32, 21 April 2015 (UTC)

Hope you do not belive in Farmville. --Hans Haase (有问题吗) 21:36, 21 April 2015 (UTC)

Does anything, besides crude oil and petroleum products, get cleaned if spilled at sea?

Are there any efforts being made to clean the sea or ocean? It's clear that some waste, like waste water, is processed before we dump it at the nearest sea. However, this is a different case. I am not asking about preventive processing, just after the fact.--ListCheck (talk) 14:31, 21 April 2015 (UTC)

Sure, see here [6], we also have a section on Ocean_Conservancy#International_Coastal_Cleanup. SemanticMantis (talk) 14:57, 21 April 2015 (UTC)

Some have proposed to filter plastic from the oceans, which tend to concentrate in certain locations. One example of a location is the Great Pacific garbage patch. There are several technical problems related to this. — Preceding unsigned comment added by 212.225.218.233 (talk) 19:12, 21 April 2015 (UTC)

We have an article on that at Great Pacific Garbage Patch. Dismas|^(talk) 19:59, 21 April 2015 (UTC)

thermal expansion

why on application of heat metals expand?Adway147 (talk) 14:41, 21 April 2015 (UTC)

Atoms in a solid interact with each other, the attractive force between two atoms is too a good approximation described by a harmonic potential, i.e. you can picture the solid as if the atoms are all connected to each other by springs. However, due to the symettry of this potential, the expansion coefficient would be exactly zero. If you raise the temperature the atoms would vibrate faster around the equilibrium points, they would deviate just as often toward being farther away as being closer to each other such that the net displacement cancels out exactly. The finite expansion coefficient is thus due to the an-harmonic corrections to the harmonic approximation of the interaction between the atoms. Count Iblis (talk) 14:56, 21 April 2015 (UTC)

In simpler terms: The atoms of all solids vibrate in place: these vibrations are what we call "heat". If we add heat, the atoms vibrate more, pushing on their neighbors more, and causing the entire substance to expand slightly. The actual mathematical and technical details are a lot more complex, and Iblis hits on many of these above. But basically, heat = molecular motion. More heat = more motion = atoms pushing each other farther apart. The fact that the effect is small is because of the counteracting effects of intermolecular forces within the solid; in gases where intermolecular forces are negligible, you'll see that an ideal gas exhibits perfect thermal expansion, where increases in absolute temperature are directly proportional to changes in volume; a concept known as Charles's law. --Jayron32 15:09, 21 April 2015 (UTC)

Seeing Hubble from 6,000 miles away

I watched a show on the National Geographic channel about the Hubble Telescope. If I heard correctly, Story Musgrave said that he spotted it from 6,000 miles away (from the Shuttle). Shouldn't the Earth be blocking the view from the Shuttle to the Hubble, if they were 6,000 miles apart? Bubba73 ^{You talkin' to me?} 15:53, 21 April 2015 (UTC)

Hubble Telescope seems to say it orbits at a height of 345 miles. I'm not sure how high the Space Shuttle was at that particular time, but probably in that same range. Can somebody do the math to figure out if two objects 6000 miles apart would be below the Earth's horizon from each other at those altitudes ? StuRat (talk) 16:03, 21 April 2015 (UTC)

Assuming orbital heights of 350 miles (and an Earth radius of 4000 miles), the HST would be well below the horizon from the shuttle -- the midpoint of that line is only about 3000 miles from the center of the Earth. While I don't know how eccentric either orbit (HST, shuttle) would have been, circular orbits at equal heights would have to be at ~1000 mile altitudes (or ~5000 mile radii) for a 6000 mile line to not intersect the Earth. Atmospheric refraction would extend the visible distance. — Lomn 16:18, 21 April 2015 (UTC)

If you assume equal heights you can put a right angle at the surface of the Earth, with 3963 miles to the center. A distance of 3000 miles means that the angle at the Earth's center is tan^-13000/3963 or a 37.1 degree angle (0.648 radians). Come to think of it, I didn't need that; I could have relied on Pythagoras to take the square root of (9000000 + 15700000) = 4970. Subtract 3963 and I get ... 1007 miles for the heights of both in order to see one another.

That said, the Space Shuttle wasn't on rails... who knows how high it was that day? Wnt (talk) 16:29, 21 April 2015 (UTC)

The Shuttle had a maximum altitude it could reach. Also, it was to rendezvous with the telescope. Bubba73 ^{You talkin' to me?} 16:43, 21 April 2015 (UTC)

Story Musgrave's Hubble mission was STS-61 with apogee 358 miles. I guess he said wrong or you heard wrong. PrimeHunter (talk) 16:50, 21 April 2015 (UTC)

You can use the Horizon distance equation to calculate the distance to the horizon for a given altitude. For 345 miles altitude its around 1687 miles to the horizon, so 3,380 miles to an object also 345 miles up. LongHairedFop (talk) 19:41, 21 April 2015 (UTC)

Presuming this is Naked Science season 4 episode 19 (18 according to some sources) Hubble Trouble, I had a quick look and couldn't find any subtitles or transcript, so finding out what was said may be difficult short of watching the whole thing again, or at least the part where it was said. (It doesn't look like season 4 was released on DVD and I'm not sure if it was ever released on VOD either and VOD can be a bit spotty with subtitles.) Nil Einne (talk) 14:56, 22 April 2015 (UTC)

I'm watching http://channel.nationalgeographic.com/episodes/hubbles-cosmic-journey/ right now on National Geographic Channel in Denmark (other countries may have other schedules). Musgrave did say: I first spotted it probably 6,000 miles away. PrimeHunter (talk) 19:49, 22 April 2015 (UTC)

We've been doing quite simple math here - can anyone tell us how much the atmospheric refraction affects the view? Wnt (talk) 21:08, 23 April 2015 (UTC)

Do the cells of multicellular organisms "think" collectively as one?

Do the cells of multicellular organisms "think" collectively as one, communicating with other cells of shared DNA in an extremely complex network, or are they really a part of a super organism that just happen to be at the right moment to do a particular job (i.e. repairing tissue damage, releasing venom)? Are cancer cells just cellular deviants, doing their own thing, or are they coded erroneously by the multicellular organism's other cells? Where does volition come in? Is volition the product of many individual cells or the product of the collective network of cells in a multicellular organism? 140.254.136.146 (talk) 16:46, 21 April 2015 (UTC)

No, they do not "think" in the sense of being sentient or sapient. But your tissues do communicate with each other through a variety of means: electrically, via the nerve system, and chemically via your blood stream using hormones. For example, let's say you just saw a lion, and the lion wants to eat you. Your brain recognizes danger, so your Amygdala sends an electrical impulse down some nerve fibers to your Hypothalamus, which secretes a series of hormones to chemically signal your pituitary gland, lying nearby, to dump a whole bunch of Adrenocorticotropic hormone into your bloodstream. This in turn signals your adrenal glands, lying on top of your kidneys, to secrete a whole bunch of adrenaline into the blood stream, which in turn signals a bunch of your bodies systems to go into overdrive, making your more likely to make it to the tree you need to climb so you don't become lion kibble. This entire Hypothalamic–pituitary–adrenal axis is an elaborate communication system going on inside your body between your tissues. However, that doesn't mean your tissues think. --Jayron32 19:19, 21 April 2015 (UTC)

Nearby cells in a tissue pass chemical signals back and forth, depending on the tissue. I'm not sure what article to reference, not Cellular communication. although there should be such an article. Volition is something at a much higher lever of consciousness. I think it is fair to say we have no understanding of volition, despite 2000 years of philosophy and science which claims to explain it. GangofOne (talk) 19:35, 21 April 2015 (UTC)

• Those are just words. Unless the distinction implies some sort of observable consequence, it doesn't mean anything. If cells were "really" part of a "super-organism", what difference would it make? If you can answer that question, then we have somewhere to begin. Looie496 (talk) 19:32, 21 April 2015 (UTC)

• Not a superorganism, just a normal organism. Perhaps a eusocial species like bees might be considered a superoganism, since the individual bees behave like cells of the hive. StuRat (talk) 20:57, 21 April 2015 (UTC)

• You may be interested in the research on Dictyostelium - just type it into google scholar, and you'll get thousands of hits - from quorum sensing to cell signalling to evolution of altruism (somewhat surprising redlink, see Altruism_(biology)). This little slime mold/amoeba is the poster child (AKA model organism) of serious research related to your question, and most peer-reviewed articles will be careful to define their terms and use language consistently. Btw, we do have an article on superorganism. SemanticMantis (talk) 21:14, 21 April 2015 (UTC)

Crops by parameters

I'd like to find some general references about what parameters do common crops need to grow. I have in mind things like temperature, altitude, amount of sun shine, chemical composition of the soil and other data like these. — Preceding unsigned comment added by 212.225.218.233 (talk) 18:31, 21 April 2015 (UTC)

It's hugely variable -- that's why people grow different crops in different places. One of the few generalities is that most crops like to get at least six hours of direct sunlight each day. Looie496 (talk) 19:28, 21 April 2015 (UTC)

Contact your local Agricultural extension. Your IP indicates you are in Spain; I don't know how to find them there, but our article suggests they may be called "Capacitación." Much of Spain has a Mediterranean climate, so that means you can grow almost anything, if you are willing to irrigate. Growing degree day is another handy search term and concept. I don't know of any good databases off-hand, but I can probably find some later. SemanticMantis (talk) 21:20, 21 April 2015 (UTC)

Think you should ask the question the other way around. By that I mean: considerer if you live in a hot dry climate with less than 30 inches of rain a year. Your soil is likely to be alkaline. In the other extreme, the northern areas of say Canada or Russia the soil on the tundra is likely to be very acidic. The same crops wont fair well in both extremes. Therefore, get your soil tested. It is not difficult to do it yourself because if I can do it so can you (it is very simple -order the kits on the internet). Then choose the crops that suit your soil. Improvements can be made by digging in manure in dry alkaline soils or adding lime to acidic soils. First things fist though – analyses your soil and choose crops to that benefit from your local rainfall and soil. For instance, if you live in a very, very dry area – don't grow maze as it is not drought tolerant. Alf Alfa would be better. If it is very very wet don't grow tomatoes as you will get stem rot.--Aspro (talk) 21:29, 21 April 2015 (UTC)

Circuit boards

What is the black, raised circle on a lot of circuit boards? I always thought it was the brain of the circuit board. — Preceding unsigned comment added by 39.176.40.2 (talk) 20:14, 21 April 2015 (UTC)

It's an epoxy-covered microcontroller, possibly custom-made for the board. LongHairedFop (talk) 20:45, 21 April 2015 (UTC)

Some Integrated circuit are dirctly bonded to the PCB. Watches, pocket games or the memory module in the picture were made this way. --Hans Haase (有问题吗) 21:33, 21 April 2015 (UTC)

For a photo of an epoxy-covered directly mounted die, see the image labeled "Figure 5-4" midway down this StackExchange discussion. I wasn't able to locate an equivalent image in commons. -- ToE 00:48, 22 April 2015 (UTC)

Further searching suggests that this style of mounting with epoxy covering is called chip-on-board with "glob top", and it is mentioned (without image) in our articles Tape-automated bonding, Surface-mount technology, & Conformal coating. An image search on "glob top" [Google] yields a lot of examples. -- ToE 01:10, 22 April 2015 (UTC)

Lordosis

If lordosis is actually non-functional and voluntary in humans, then is there any reflexive behavior that is actually functional in the human female during copulation? Perhaps, human copulatory behavior involves a series of voluntary, non-reflexive behaviors? Why did human females lose the reflex, and how did this impact the motions of copulation? 140.254.136.178 (talk) 20:46, 21 April 2015 (UTC)

I doubt "human" females lost the reflex, I suspect the reflex is useless once you start down the bipedal path and it was lost before we were human. If it was lost it obviously confers no or little survival or procreation advantage, I doubt there's much more of a "reason" than that. "How did it impact the motions of copulation?" I honestly can't work out what an answer to that question might even look like. The reflex would have been lost BECAUSE the motions evolved, not "the motions evolved becuase the reflex was lost". Vespine (talk) 22:53, 21 April 2015 (UTC)

Have you considered signing up for a Hygiene class at Ohio State? I bet they could answer a lot of the recurring questions you pose here. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:56, 21 April 2015 (UTC)

P.S. This is a sincere comment. Don't delete it again. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:05, 21 April 2015 (UTC)

"Reflex" is a concept that seems simple but turns out to be very tricky when you try to pin it down. What really matters is whether a behavior is genetically programmed or learned. It's clear to me that there are many aspects of both male and female copulatory behavior that are so consistent that they surely must be to a large degree genetically programmed -- most obviously, the basic rhythm of copulation. Looie496 (talk) 22:57, 21 April 2015 (UTC)

Yikes! Please do not confuse innate responses with reflexes (and I am not sure what "genetically programmed" means). A reflex action is one which bypasses the brain, e.g. immediate withdrawl of a finger which touches a hot surface. An innate response may involve the brain, e.g. being scared of snakes.DrChrissy ^(talk) 23:23, 21 April 2015 (UTC)

This is just the sort of thing I meant when I said that the concept of a reflex is tricky. The word "reflex" is commonly used for many responses that involve the brain, for example the optokinetic reflex, in which the eyes automatically move to track a moving object; or the pupillary light reflex; or the accommodation reflex. Looie496 (talk) 14:08, 22 April 2015 (UTC)

• Get Lowrdosis, NOT SAFE FOR WORK or KIDS version. μηδείς (talk) 20:33, 24 April 2015 (UTC)