Wikipedia:Reference desk/Archives/Science/2015 February 9

= February 9 =

What percentage of people are medically excluded from getting vaccines?
Vaccines are an essential part of modern medicine. However, in stories discussing the current measles outbreak in the US they mention that some people are not eligible to receive the vaccine. The largest category of people who are medically excluded is infants under 1 year of age, but they also mention that children with compromised immune systems or allergies to any vaccine component would also be ineligible to receive the vaccine. As a percentage of the US population, how large is the set of people that would be unable to receive the vaccine due to a medical reason like this? Aside from the infants under 1 year of age, I would guess that the other medically excluded groups would be fewer than 1 in 100 children, but I haven't been able to find any statistics. Dragons flight (talk) 03:59, 9 February 2015 (UTC)


 * This gives a "conservative estimate" of 1% of British kids allergic to eggs. Unless there are no other allergens in there, the same convenient "1 in 100" probably works for Americans, too. So 3,160,000 flu corpses. Thanks a lot, eggs. InedibleHulk (talk) 04:21, 9 February 2015 (UTC)


 * You're forgetting about herd immunity. So long as 99% of the population is immune, due to vaccines, the disease won't be able to spread.  However, when you add in all the people who don't get vaccines, and the ineffectiveness of the current vaccine, things get a lot worse. StuRat (talk) 04:26, 9 February 2015 (UTC)
 * It could theoretically jump in one unbroken line between all the unimmune, through chance encounters. Statistically unlikely, but weird stuff happens. I'm staying optimistic. Also, herd mentality (I hear you get it from Chinese beef) might cause the clean to "clean up" the unclean, if it ever truly gets to 99% (no margins of error). InedibleHulk (talk) 04:40, 9 February 2015 (UTC)


 * 99.7% of kindergarteners are fully vaccinated in Mississippi, which doesn't allow parents to opt out. In West Virginia, which apparently has a similar law, only 97% of children aged 5–18 are vaccinated. One possible reason for the discrepancy is that Mississippi requires immunization for public and private school students, while West Virginia may require it only for public school students ( - it's not entirely clear). -- BenRG (talk) 04:26, 9 February 2015 (UTC)


 * Thanks. That comparison is very informative.  Dragons flight (talk) 07:09, 9 February 2015 (UTC)


 * A key fact about the nature of the spread of these diseases is that the rate of spread (and whether they spread at all) is very sensitive to that percentage. It's not a linear relationship between the number of unvaccinated people and the number of cases of the disease.  It only takes a few percent difference in the vaccination rate to go from no disease to an epidemic.   The fact that there always will be on the order of 1% who simply cannot be vaccinated makes it all the more critical that we get all of the remaining 99% done because it only takes another couple of percentage points of people who don't do it to push the system over the edge into an epidemic.  Since kids can't be vaccinated safely until they are several years old, that could cause horrific problems for babies and toddlers.  That's especially true of Measles because it spreads so much more easily than most other diseases...and each dose of the vaccine only delivers a 95% chance of protecting you.   That's why it's recommended that children get two doses because then only one in four hundred properly vaccinated kids are left without protection.


 * When you consider the (maybe) 1% who can't be vaccinated plus the only-had-one-dose children who probably make up at least that many more who are unprotected, plus the 1-in-400 properly vaccinated who aren't immune...and then the numbers start to get alarming. I'm old enough to actually have had the measles when I was a kid...I was probably one of the last before the MMR vaccine became available in the UK.  It's really no fun!   Not only is the disease itself pretty nasty, but it also knocks out your immune system for several weeks after you recover from the Measles virus itself.  So you tend to get over the measles - and then go down with a cluster of nasty colds and flu's for weeks afterwards.   We didn't know that when I was a kid - so I was sent back to school as soon as the measles rash had gone away. SteveBaker (talk) 16:52, 10 February 2015 (UTC)


 * The second image in this article explicitly shows permanent medical exemptions for California kindergarteners. The rate seems to hover around 0.1%–0.2%. -- BenRG (talk) 20:33, 11 February 2015 (UTC)


 * Another 1,200,000 are doomed via compromise with HIV, and it's going up. Apparently, there are 149 other immune disorders. I don't want to count that high. Aging itself compromises the system, but there's no set rule to how old is old. And most agencies wouldn't count that as "compromised". InedibleHulk (talk) 04:30, 9 February 2015 (UTC)

500-megahertz quartz oscillator meme
(These are two links.) Somehow, it became "well-known" that a quartz crystal like the ones in clocks have a frequency of 229 hertz, about 537MHz, but our article says otherwise: that it's only 215 = 32768Hz, and that these crystals are designed that way because the frequency would be higher (single digit MHz) otherwise.

Now, my questions:
 * What advantages do the low frequency crystals provide? One, they are not temperature-compensating, and two, the cut is quite complex; the only thing I could think of would be that the difficult cut is still cheaper than a high-speed counter which can handle the millions of pulses per second a cheaper crystal would emit, and the amount of T-frequency shift is still acceptable for everyday use.
 * Does anyone know where that meme originated? Extremely high frequencies are not only undesirable, but 500MHz are higher than anything a quartz oscillator any quartz oscillator listed in the article could acheive (the highest listed frequency is 300MHz).

Thanks in advance. - ¡Ouch! (hurt me / more pain) 10:54, 9 February 2015 (UTC)


 * The 32768 Hz frequency dates back to at least the early days of digital wristwatches. I don't know if it was the real reason behind its choice, but CMOS circuits draw most current during state transitions. A low frequency helps conserve power—something very important for a wristwatch. --173.49.18.95 (talk) 12:51, 9 February 2015 (UTC)
 * That seems to be it! I completely forgot about the battery issue. - ¡Ouch! (hurt me / more pain) 07:05, 10 February 2015 (UTC)
 * In regard to your second question, 500MHz is achievable in quartz. The 32768 Hz frequency is a bulk acoustic wave resonance. Thinner crystals allow for higher bulk frequencies, but not up to 500MHz. To go that high, you need a surface acoustic wave oscillator. This paper gives a simple account of the ideas behind SAW oscillators. --Mark viking (talk) 01:04, 10 February 2015 (UTC)

Thanks IP 173.48 and Mark viking. That answers my questions except the origin of the misconception that quartz clocks run at 537MHz. Maybe somebody wrote that "frequencies around 500MHz are used for highly precise clocks" and "quartz clocks are more precise than mechanical clocks", and somebody else merged that into the false "quartz clocks run at 537MHz" meme. - ¡Ouch! (hurt me / more pain) 07:05, 10 February 2015 (UTC)

Contact Jean Meeus
I have a question regarding a paper written by Jean Meeus that I would like to have him provide the answer. Specifically, what are the equations, parameters and initial conditions for the tabulation of the tropical year lengths given in the reference below? How do I contact Jean Meeus? Kpenwarden7 (talk) 11:20, 9 February 2015 (UTC)


 * You will find his address on page 42 of the paper here. Click on the link at the bottom for "Next article page" twice. Richerman    (talk) 14:57, 9 February 2015 (UTC)


 * His email address (as of 2011) is provided at the bottom of the second page of this more recent article (nominally p. 32). Please remember to be polite when contacting the author of a scientific paper, and it will help to send from a .edu address, as well as containing a brief description of why you are interested in the information. SemanticMantis (talk) 16:32, 9 February 2015 (UTC)
 * .edu addresses only exist in the US. The general advice is to avoid using GMail and the like, and instead use institutional addresses. 131.251.254.81 (talk) 17:44, 9 February 2015 (UTC)
 * That's not true, see .edu. There are many non-USA .edu addresses. But I suppose that's still a good point, an address associated with a school or research institution is what I meant and should have said. For instance the second-level domain .ac would do just as well (e.g. .ac.uk), or even stuff like .edu.cn, which China uses for educational addresses. SemanticMantis (talk) 20:08, 9 February 2015 (UTC)

Three cars colliding
Many years ago, before cars were designed to crumple, I was driving the middle of three cars all of us going too fast along a city street. The first car stopped suddenly and I braked hard and managed to stop only about a foot (or less) behind. The last car crashed into me and my car was shot forward to hit the first car. The first car was not damaged at all (!), my car was somewhat damaged front and back and the last car was quite severely damaged. Was the differential damage due to differences in mass or construction of the cars or whether their brakes were on at the time(s) of impact? If the three cars had been identical what would have been the damage situation? Thincat (talk) 14:14, 9 February 2015 (UTC)


 * How can we know? There are so many confounding factors, we can't possibly answer without resorting to wild speculation.
 * Here's a link to Crashworthiness Research at the NHTSA. The "Aggressiveness and Fleet Compatiblity" division is dedicated to studying competitively-engineered vehicles.  If Company A starts building and selling armored cars to improve safety, passengers who drive vehicles made by Company B and C may become less safe.  So, there's a huge amount of research on this topic, as it pertains to basic science, vehicle safety engineering, and public policy choices.  Nimur (talk) 16:10, 9 February 2015 (UTC)


 * I think not having brakes on when rear-ended may help the front car, since it can then accelerate to handle the inertia transferred from the other car, rather than crumple, to use up that energy. StuRat (talk) 16:18, 9 February 2015 (UTC)
 * Sort of a giant Newton's cradle, only they don't go back again (hopefully). Alansplodge (talk) 16:36, 9 February 2015 (UTC)
 * I don't think you need wild speculation, especially in the 'what if all the cars had been identical' case; you just need to state your assumptions. Is a Newton's cradle a good model to explain the energy transfer? If not, why not? 2A01:E34:EF5E:4640:11D0:F415:10CF:7542 (talk) 18:18, 9 February 2015 (UTC)
 * The Newton's cradle will probably not fit well, because car accidents are inelastic collisions. The energy lost will mainly go into deformation. If we're stuck with 3 identical cars, the first stationary and the last moving at velocity v, we should have the least damaging situation with the middle car moving at v/2, and hit the first car at the same moment as being hit by the last car. Both collisions will happen at an effective velocity of v/2.
 * No, wait, that's not assuming the cars are identical but that the second car can take the same amount of abuse from both ends. The v/2 situation is highly symmetric but not necessarily the least damaging overall. It's not practical either; you'd probably want to minimize the kinetic energy to minimize collateral damage from cars spinning out of control if the velocities are not perfectly parallel. - ¡Ouch! (hurt me / more pain) 07:18, 10 February 2015 (UTC)
 * Yes, it's more like Newton's cradle with spheres made of putty, and there's also the issue of how firmly the brakes are applied.   D b f i r s   07:31, 10 February 2015 (UTC)


 * I agree that the brakes are a key matter here - but it's not a simple situation.


 * But let's step back a moment and consider a two-car situation: If car A hits car B in the rear then if B has no brakes applied then much of the energy of the collision would go into accelerating it forwards, reducing the amount of energy available for deforming metal on both vehicles.  However, that's only considering damage to the two cars...in terms of damage to the people inside the car, you want to minimize acceleration applied to them because that's what does the damage.  Having the brakes applied forces more of the energy into deforming metal and heating up the brakes and less into accelerating car B forwards...which is good for the people inside car B...but for people in car A, it's resulting in more violent deceleration - which is worse for both the car AND the passengers.   So brakes or no brakes on the front car is a mixed blessing!


 * B has brakes on: Car B takes more damage, so does Car A.   Car B's passengers take less damage, but Car A's passengers take more.
 * B has brakes off: Both cars take less damage, car B's passengers take more damage, car A's take less.


 * Now let's think about the three car case.  This splits into two possible scenarios:


 * A hits B which then rolls forwards and hits C, which is just two separate two-car collisions: A-to-B and then B-to-C.
 * A is still in contact with B when it hits C...then we still have (in effect) two two-car collisions: A hits B and then the combined mass of A+B hits C.


 * These are subtly different situations.


 * In the first case, the A->B collision is adequately explained above...but the B->C collision depends on how fast B is moving as a result of the A->B collision.  If B's brakes were on during A->B then B's forward speed when it hits C will be less - which is obviously good for all concerned...and the state of C's brakes must be considered per in my explanation, above.


 * In the second case, we have to consider the combined A+B mass as well as its velocity...and that combined mass is much greater than B alone - so there is much more kinetic energy in the collision with C. As before, if the impacting car is braking (in this case, either B alone or A and B, then that's better for all concerned...but the state of C's brakes affect the outcome.   When B hits C, both cars have to absorb A's momentum - so B's rear-end gets crushed some more and C absorbs some additional momentum because of that.   B is not happy though.  Regardless of whether his brakes were on in the initial A-B collision, he's now going to take additional damage depending on how C's brakes are set...so that's clearly a worse situation than merely an A-B or B-C collision alone.


 * Suffice to say that the analysis here is complicated. It's made worse by the fact that people's feet may slip off the brake when the impact happens...unless maybe they have the parking brake set.  If the car is a stick-shift and the driver has his/her foot on the clutch and that foot slips off and the car is still in gear.  Then what if your foot is lightly resting on the gas pedal and being rear-ended forces your foot down onto the brake pedal harder.   There are an insane number of complicated things going on here.


 * So analyzing what happened in one particular case - even with identical cars - is exceedingly complicated.


 * To illustrate real-world complexity: The last time my car got rear-ended, the impacting vehicle was a Dodge RAM (well named!) pickup towing a gigantic travel-trailer. This was on a freeway, where the traffic had abruptly slowed down for some reason. The police said that the driver (who's fault this was) left no skid marks and so was probably going at 50mph at the time.  My MINI Cooper and the car in front were both stationary, and about 10 feet apart.  I'd been braking to a stop, so PROBABLY I had one foot on the brake and the other on the clutch...but I hit the car in front with enough of an angle to spin my car around about 45 degrees...sticking the front of my MINI out into the adjacent lane...where I got hit again by another car that was still going quite fast.   That somehow pushed me backwards onto the shoulder where yet another car had pulled over onto the shoulder in order to avoid rear-ending the Dodge RAM's trailer - and he whacked me on the back end, resulting in my car facing 180 degrees the wrong way.  When yet another car rear-ended the now stationary Dodge, he hit me again and I wound up with the front end of my car wedged under the FRONT of the pickup.  A total of 9 cars were involved.


 * Explaining to the insurance company how I ended up being both front *and* read-ended by the same vehicle took quite some work!  My car was written off with every single body panel crushed quite impressively.  The driver-side door opened without problems and I stepped out with nothing more than some scrapes to my forehead from the roof liner and a horrendous case of whiplash.  The towtruck driver was actually able to drive the MINI up onto the bed of his truck.  None of the six airbags in my car went off...which is good because none of them would have helped.


 * This is more typical of the chaos involved than the clinical "A hit B hit C" situation. SteveBaker (talk) 16:00, 10 February 2015 (UTC)


 * Incidentally, the issue of whether you should stand on the brakes or not when you see a car about to rear-end you is an interesting ethical matter. Theoretically, applying the brakes helps you, but worsens things for the person hitting you.   For most of us, we don't have the time to think this through before it's too late - so there isn't much of an issue involved.
 * But for a self-driving car of the near future, this is a very tough moral and legal dilemma.  The car's computer has PLENTY of time to calculate the speed of the oncoming vehicle, maybe in future even send a radio signal to the other car's computer to tell it to slam on the brakes.  It could maybe have time to query the other car for model number and thereby know the mass of each car by asking the incoming vehicle to report this data back to it.   But the ultimate decision of whether to protect its own passengers at the cost of increased injury to others is the kind of problem you'd expect Isaac Asimov to be writing about!  Things could get even more complicated if the computer has access to the sensors in the seats that tell it which seats are occupied (my car has this already for seatbelt warnings and airbag-launch decisions) - it could discuss with the oncoming car the number and, perhaps even the weight and height, of it's passengers and deduce that one of these people at risk is a small child.   In the several billion instruction cycles it has in the last second before the crash, it can reason through a huge  number of options...but in the end, some computer programmer has to decide the policy of who gets to live and who gets to die.
 * ". . . the kind of problem you'd expect Isaac Asimov to be writing about!" Well, we aren't going to dig him up just for that! {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:11, 11 February 2015 (UTC)
 * It could get even deeper, suppose each car also knows the name of the insurance policy that it's covered by - and the terms of that insurance. Should it try to protect the people who have the least good health insurance at the cost of additional damage to those who have a smaller co-pay?   Or maybe vice-versa if the insurance companies insist on it! SteveBaker (talk) 16:17, 10 February 2015 (UTC)
 * Interesting considerations! This merits a new question: WP:RD/H &mdash; Sebastian 02:11, 11 February 2015 (UTC)

OP here. Thank you very much for all those very interesting answers. Brakes are clearly a major consideration because they affect the way the original kinetic energy is either transferred to other vehicles or converted to heat in the brakes themselves or in the deformation of the cars. I'm amazed at Steve's presence of mind in being able to analyse what happened in his crash. I don't even know if I had my brakes on in my collision and I strongly suspect I didn't know even at the time. Thincat (talk) 09:39, 11 February 2015 (UTC)
 * The impact of the brakes is probably not that huge.
 * Brakes don't tend to stop a car within about 10 meters unless you're not going that fast in the first place. At 80kph (~50mph, 22m/s), I'd be surprised if it were within 30m (~100ft). Accidents on the other hand bring the cars to relative rest within one meter (~3ft), except when they don't (if the collision isn't head-on or is extremely violent.)
 * Using these rough figures, braking will make hardly more than a 6% (6 in 100, the "other" 3 in 100 coming from the distance B and C had before A hit B; I'm using 3ft here) difference. The brakes will most likely be overwhelmed immediately, and the major difference in damage observed could be the damage to the brakes themselves. Of course, there could still be the difference between death and "only" serious injury... and things would change with a longer gap between B and C.
 * OTOH, if A hits B and C, who don't move initially, violently enough to push B against C, wouldn't A's death be the more ethical outcome (for certain values of "ethical") in the long run? - ¡Ouch! (hurt me / more pain) 12:03, 11 February 2015 (UTC)

Leak repair
I have a small leak in the drain pipe from a shower, near to the outlet but inaccessible without a lot of damage. I assume that the white pipe is of PVC. Is there anything which could be poured down to leave an effective coating on the inner surface and any grooves in the joints, stopping the leak but unaffected by lukewarm soapy water and proprietary sludge removers? If no such material is available over the counter, could it be made from readily-available components?→31.54.246.96 (talk) 17:36, 9 February 2015 (UTC)


 * As a shower can be likened to a vertical swimming pool that never fills up, you could try this stuff for sealing leaky pipes. Swimming pools have lots of more nasties in them than soap and detergent – such as alum, sodium hypo-chloride, your neighbors kids pee, Coca Cola ad infinitum. --Aspro (talk) 19:24, 9 February 2015 (UTC)
 * There are similar gunks sold for stopping leaks in car radiators...although those *might* rely on the heat from the water to help them cure...I'm not sure. SteveBaker (talk) 16:35, 10 February 2015 (UTC)


 * If you have a leak, you should definitely consult a professional plumber. I can tell you from bitter experience that what may seem like a small leak can actually be much worse than it looks - and the longer you let it go, the worse (and more espensive) it will get. ←Baseball Bugs What's up, Doc? carrots→ 00:31, 10 February 2015 (UTC)


 * I agree. Mold growth is a particular issue with long-standing leaks - and that can pose a health risk.  If your leak has been around for a long time, you should probably get it fixed properly so that all of that consequential damage can also be cleaned up. SteveBaker (talk) 16:35, 10 February 2015 (UTC)


 * To the OP: How do you know the leak is near the drainage if not easily accessible? What triggered your awareness of a leak or where is water coming out inside the house if any? Is your house raised or build on ground with a concrete slab? I assume you're in the US(?) but if not you should let us know. Makes a difference b/c of building codes and usual set-ups (even when not up to code).TMCk (talk) 01:35, 11 February 2015 (UTC)


 * (OP) The shower is upstairs, in the UK. The leak was detected by a spreading damp patch on the downstairs ceiling almost directly below the outlet, hence the known proximity. The only convenient access is from the front of the shower tray, the outlet being at the back. The gap between tray base and floor permits only an arm to enter, which can just reach the outlet. Neither feel nor vision shows any moisture, so the escape must be below, in the space above the downstairs ceiling. The shower is not in regular use, so it's not possible to say how long the problem has been there. Finally, a plumber is coming to take a look tomorrow.→31.54.246.96 (talk) 15:45, 11 February 2015 (UTC)


 * Bummer that you're not in the US. Even so I know something about (Western) European construction, it is limited to certain countries and Britain is not one of them. For now you do rely on your plumber's expertise and hope he has some equipment to pinpoint the leak. Thermal imaging would be the most reliable one tho there are other options. If your floor containing the leaking pipe is of solid concrete, thermal imaging is the best and most accurate. If it is timber build and hollow besides noise insulation it's possible to take a look with a snake like camera, like cheap USB ones to be used with a PC/laptop or a professional one with built in screen. Also a true fix could be done in the latter case from below by cutting into the ceiling where drywall or plaster is applied to wooden 1x2's or similar. If it's solid concrete it's usually the best way to chip in from the top. Using the pool leaking stuff mentioned above would be difficult since you'd have to plug the drain somewhere below the leak and still be able to fill the pipe while draining out some plain water below. Also I'd say that if it doesn't seal 100% (which is not a real problem when it comes to a pool), the problem will be just postponed but not solved. Wish you good luck with your plumber since you need an experienced one to have your drainage fixed. Feel free to post on my talkpage if you have any questions now or later and I'll try my best to help you out. This page is on my watchlist but I pay little attention to it and responses might take longer than needed. Cheers and hope for the best, TMCk (talk) 01:48, 12 February 2015 (UTC)

Before pasteurization, did people drink milk from livestock?
Before pasteurization, did people drink milk? How safe was it? How long was the shelf life? Where did people store milk? 140.254.226.195 (talk) 20:33, 9 February 2015 (UTC)


 * This article deals with the history of milk consumption. You have to be specific when saying milk though. I assume you're talking about cow's milk, but you could also be talking about goat's milk, water buffalo milk, or the milk you, and most of the rest of us, got from our mothers as babies. Sir William Matthew Flinders Petrie &#124; Say Shalom! 20 Shevat 5775 20:40, 9 February 2015 (UTC)


 * We've been drinking other mothers' milk since the Neolithic Revolution. It was safe enough, considering most people drank it soon after getting it from their own cow (or yak, whatever). Freshness didn't need to last. Once things started going urban, the cow-to-mouth time and distance got long enough to spoil things for a while. The shelf live was probably what it is now, a day or two. They kept it stored in cow jugs for the most part, clay jugs for the meantime. InedibleHulk (talk) 20:41, 9 February 2015 (UTC)


 * I see what you did there. Sir William Matthew Flinders Petrie &#124; Say Shalom! 20 Shevat 5775 20:45, 9 February 2015 (UTC)


 * Shouldn't change other people's headers, sir. If you think they mean something, best to just ask. Now your reply implies our mothers might be included by "livestock". InedibleHulk (talk) 20:57, 9 February 2015 (UTC)


 * Ah damn, didn't realise that was poor wikiquette as I keep seeing people do it. I'll remember for the future though, especially so as to avoid implications of livestock status towards editors' mothers. Sir William Matthew Flinders Petrie &#124; Say Shalom! 20 Shevat 5775 21:01, 9 February 2015 (UTC)


 * And, of course, some people died of things like Bovine TB before pasteurisation. It wasn't just about avoiding spoilage. 86.175.86.97 (talk) 20:59, 9 February 2015 (UTC)


 * The drowning risk has slightly increased with industrialization. InedibleHulk (talk) 22:30, 9 February 2015 (UTC)


 * Reminds me of that slave preparing Cleopatra's bath of asses milk. He poured so much in, that instead of having it up to her chin, she had it past-'er-eyes.--Aspro (talk) 22:54, 9 February 2015 (UTC)


 * Laughed my asp off! InedibleHulk (talk) 23:11, 9 February 2015 (UTC)


 * "This tub smells like ass !" StuRat (talk) 23:58, 9 February 2015 (UTC)


 * One way people stored milk before pasteurization was cheese. SemanticMantis (talk) 22:24, 9 February 2015 (UTC)
 * Would agree with that. Back then, cheese was an important food source for the winter. Also, the time of the year when cows produce gallons off the stuff, is the same time of the year when other nutrition becomes plentiful. So turn it into cheese. There was limited rapid transport from the rural areas to the towns and most folks could not afford tea nor coffee. Most butter was hand-churned and was thus expensive – bread-an'-drippin' was cheaper and more tasty.--Aspro (talk) 23:13, 9 February 2015 (UTC)


 * Oh, kids to-day don't know what their missing! This English chef is bringing working-class 'bread and dripping' to his finest patrons Plus a little bit of meat-jelly from the bottom of the bowl and a little bit of salt and pepper -uhmmmm yummy!--Aspro (talk) 23:23, 9 February 2015 (UTC)


 * Yes, many people did (and many in the world still do) drink unpasteurised milk. I recall holding my mug under a cow as it was being milked by hand, and drinking the milk warm, but that was many years ago.  Milk kept for a couple of days if stored somewhere cool, maybe three days in winter, but it needed to be cooled as soon as possible for best keeping quality.  The risk of Tuberculosis was present, and some people died from consumption through drinking milk, but human strains of the disease caused many more deaths.  Bovine tuberculosis was less common in cows in those days, and people just didn't worry about it.    D b f i r s   23:13, 9 February 2015 (UTC)


 * When were "those days" when people didn't worry about bovine TB? My grandparents had stories of peers who died in childhood from it, and it was clearly still a little raw even in their 70s. 86.175.86.97 (talk) 05:53, 10 February 2015 (UTC)


 * Lots of people still drink Raw milk today. I live in the UK and we used to drink it in the 1970s. It was delivered in bottles (with green foil tops) to our doorstep direct from the farm. The herd had to be accredited as being free of tuberculosis and brucellosis. It kept fine for two or three days in the fridge and the amount of cream on top varied according to the season - in the spring and summer when the grass was lush there was tons of it. In those days cream was good for you! I believe you can still buy it today as a niche product but I've not seen it for years as, like most people, we buy ours from the supermarket in plastic cartons. Back in the 1950s I remember we had a terracotta earthenware cover that sat in a saucer of water and kept a bottle of milk cool by evaporative cooling. There was also a pantry with a stone slab to keep things cool. That's also about the time that Aspro's joke about Cleopatra dates to :-) Richerman    (talk) 23:14, 9 February 2015 (UTC)
 * I too, haven't seen 'green tops' since about the late 1970's. The nice thing was, that the milk was not homogenized and so one got  the cream at the top which one doesn't get these days. The unglazed terra cotter coolers were also ubiquitous (before we recover from the post-war recession and could afford fridges). Sorry about the  Cleopatra thing but you can't teach an old dog new jokes, yet you must admit,  the  InedibleHulk did asp for it ;¬ )--Aspro (talk) 23:55, 9 February 2015 (UTC)
 * In NZ you can get silver top milk which isn't unpasteurised, but also isn't homoginised in probably most big super markets. Raw milk can only be purchased from producers AFAIK . . Nil Einne (talk) 01:32, 10 February 2015 (UTC)


 * Another old school danger of straight cow milk is when you're four and walking them home and are mysteriously slain. Like in the story below the one in the "drowning risk" link above. And Kellogg's partner died. That newspaper is bad news for milk, all around.
 * More commonly, I guess the cow could kick or fall on you while milking. Or burn down Chicago. Or blow up a shed in Rasdorf with farts. InedibleHulk (talk) 23:26, 9 February 2015 (UTC)


 * Yes, I concur. Cows are really big animals when you get up close to them – or they get up close to you. Yet, they are peaceful creatures, so if one of us   finds  we are   pushing up the daisies – it not the cows fault.--Aspro (talk) 00:08, 10 February 2015 (UTC)
 * Talking of milk, do any of you remember 'prohibition' ? No, nether do I -as I was too drunk. Nellie Wallace however, had a top-ten hit back then. Let's have a tiddley at the milk bar. Wonder if its available on iTunes yet?--Aspro (talk) 00:21, 10 February 2015 (UTC)


 * Cows may normally be docile, but they have horns and they know how to use them. ←Baseball Bugs What's up, Doc? carrots→ 00:29, 10 February 2015 (UTC)


 * Other than on heredity herds, I haven't seen any horns...Livestock dehorning. How can they use what they haven't got and when you give them no reason to use what they haven't got? --Aspro (talk) 00:37, 10 February 2015 (UTC)
 * They wouldn't necessarily "know" that their horns are missing, and just a good sideswipe by the head could knock someone over. ←Baseball Bugs What's up, Doc? carrots→ 00:41, 10 February 2015 (UTC)
 * Just getting knock over is a hell of a lot different to getting gorged.--Aspro (talk) 01:00, 10 February 2015 (UTC)
 * Depends what you land on after being whacked. ←Baseball Bugs What's up, Doc? carrots→ 01:11, 10 February 2015 (UTC)
 * One can get gorged on beef, but not gored. μηδείς (talk) 01:07, 10 February 2015 (UTC)


 * It's off-topic, but cows definitely do kill people. Apparently about 22 farm workers are killed by cows per year in the U.S. . A few hikers are trampled to death by cows every year . -- BenRG (talk) 07:34, 10 February 2015 (UTC)
 * Not off-topic. One question was about safety. If you want fresh milk, the cow is not optional. Tried looking for dangerous yak stats, but not much luck. Could be the relative lack of oversight where they live, or that they generally have more room to avoid the farmer. They don't call it a squeeze chute or livestock crush for nothing. Even away from there, plenty of fences and stall walls on the typical Western farm. InedibleHulk (talk) 23:09, 10 February 2015 (UTC)

My family used to get raw milk from a farmer in a village in Normandy when I was small (we had a vacation house there). Usually we would leave a milk can in his barn in the evening, and in the morning we would pick it up with the milk from the morning milking in it. Sometimes us children would even just walk down to his field when he was milking the cows and he would fill up the can right there. One year, he told us that he wouldn't be able to sell us milk anymore, since there was now a law against selling unpasteurized milk. I think he also mentioned that someone in the village had reported him. This was sometime around the year 2000. We also got our milk back in Germany straight from the farmer, but I'm not sure it wasn't pasteurized already. The milk from both farmers definitely had a much richer taste than the milk you get from a store nowadays, as well as the cream on top others have mentioned already. --Terfili (talk) 14:18, 10 February 2015 (UTC)


 * My great-uncle and great-aunt ware a dairy farmers in the UK (near Norwich) - when I stayed with them as a kid, we'd always get unpasteurised milk straight from the cow. I *hated* it because it was never cold...cow-body-temperature milk is absolutely disgusting!  However, what's interesting is how he stored it for their own use.  They'd use a large (about a gallon maybe) unglazed ceramic jug.  The water from the milk would gradually soak through the ceramic and evaporate off the surface - and this would cool the milk quite well.   They'd fill the jug with boiling water at the end of each day.


 * But when you have your own cow(s), they have to be milked twice a day to avoid their milk drying up...so the idea of having to keep the stuff for more than even a few hours was kinda silly. So in any primitive society, the idea of milk being stored for more than a day or so just doesn't make sense.


 * If you wanted fresh milk, you always had some that was less than maybe 8 hours old - and whatever you didn't drink either got mixed in with the pig swill or churned into butter or cheese.


 * As a mixed-use farmer, he had a pretty small herd - but just one of those cows was used for milk for the family. She was more like a pet than a farm animal - and although different cows took the role over the years, the family cow was always called "Buttercup".  I suspect that the logic behind this was that you wanted to be rather more careful of how your own, unpasteurized milk was obtained than with the bulk milking you did to send off to the pasteurization plant every day...and it would be relatively easy to spot signs of disease in Buttercup compared to the rest of the herd.


 * Another point that occurs to me is that the farmers back in those days had close contact with their cows (especially if they were hand-milking them) - so any diseases that the cows had that was transmissible to humans would get transmitted regardless of drinking the milk.  I'd expect that these people would rapidly build up an immunity to whatever bugs the cows might be harboring.  The problem only becomes unmanageable when you drink milk from other people's herds.


 * SteveBaker (talk) 15:14, 10 February 2015 (UTC)
 * When one is most used, to chilled milk straight from the fridge, then fresh milk straight from the cow, goat etc., may taste odd. But milk straight from the fridge tasted odd to me. It had lost its original favor. Also, cows don't have to be milked twice a day. Great cheese comes from once a day midday milking -because it is richer. From what I can remember 'buttercup' was a term of endearment; given to the cow that was the highest milk producer – got to stop here because the wife is sending me those knowing glances (filled with daggers!!!) and as I'm not I mind-reader I don't want she is tying to say. Other than I used to call her Buttercup – a along long time ago.--Aspro (talk) 19:15, 10 February 2015 (UTC)
 * Yes, and in the case of cowpox, catching it provides immunity for the much more serious smallpox, so could be considered a good thing. Indeed, smooth "milkmaid's skin" was due to the lack of smallpox scars on the face. StuRat (talk) 15:27, 10 February 2015 (UTC)


 * A few points addressing the OP's first two questions:
 * Humans have been consuming dairy products for about 10,000 years, and many of them have been drinking milk for about 6,000 years (after a genetic mutation allowed adults to tolerate lactose). Since pasteurization dates back to only the 19th century (though milk was sometimes heated even before then) and became widespread only by the middle of the 20th century, for most of human history milk was consumed without pasteurization.
 * Milk consumption by the populations that could tolerate lactose during adulthood gave them a significant evolutionary advantage. See details in this Nature News writeup, which notes that "In a 2004 study, researchers estimated that people with the mutation would have produced up to 19% more fertile offspring than those who lacked it. The researchers called that degree of selection “among the strongest yet seen for any gene in the genome”."
 * But drinking unpasteurized milk was not without its dangers. For example this 1943 article estimates that in England and Wales alone, drinking unpasteurized milk caused 65,000 deaths due to bovine TB during the 1912-1937 period and many more due to other diseases. And this AAP statement notes that, "Before pasteurization of milk began in theUnited States in the 1920s, consumption of raw dairy products accounted for a significant proportion of food-borne illnesses among Americans and resulted in hundreds of outbreaks of tuberculosis and infections caused by bacteria, such as Brucella abortus, streptococcal species, and enteric pathogens."
 * Abecedare (talk) 20:46, 10 February 2015 (UTC)
 * When I was a child we had a cow and certainly enjoyed the fresh milk. She was a sweet-tempered little Jersey and the milk was very high in butterfat. We had a refrigerator. In my grandparent's day the milk was kept in a springhouse or in a metal can lowered down into the well. Edison (talk) 21:08, 10 February 2015 (UTC)
 * That would be a springhouse - something I've never heard of before. You learn something every day Richerman    (talk) 09:23, 11 February 2015 (UTC)


 * Despite the small risk (which can be fatal of course), there is nothing better than the taste of real fresh raw milk. Those who don't like the taste just are used to what they get at the store. Pasteurization makes milk safe or safer but unfortunately also kills parts of raw milk that are good for you. Anyhow, here in the US you can only get/buy it officially labeled "for animal consumption only".TMCk (talk) 02:07, 12 February 2015 (UTC)
 * Fit for the most dangerous animal of all...box jellyfish! That site may or may not understand how Top Ten lists work. InedibleHulk (talk) 03:18, 12 February 2015 (UTC)

At user:Edison: What happened to the "sweet-tempered little Jersey"? Guess she ended up as meat for consumption but what about offspring? Did she had any? :) TMCk (talk) 02:37, 12 February 2015 (UTC)


 * As per others, about 20 years ago I was still milking a cow every day. My family used the milk (largish family - five or six litres of milk were used every day).
 * Following the discussion on dangers above, while it's true that most cattle have their horns removed, they don't typically have their hooves removed, and that's where I'd say the main danger lies. They can kick and kick hard, and a large cow or bull is quite capable of getting a hoof to a lowish head height on a human.  They also weigh quite a bit, and once they've knocked you over they are perfectly able to trample you to death, especially if there's more than one of them.  GoldenRing (talk) 03:17, 12 February 2015 (UTC)


 * Tho pasteurization didn't prevent that danger. hey, you wanna have real fresh milk you still have to take a chance... :)) TMCk (talk) 03:41, 12 February 2015 (UTC)

A friend of mine grew up on a farm many decades ago. He said that he drank raw milk as a child, but knew which cow it came from and could see that "his" cow was healthy and properly milked. His idea is that commingling the milk from many cows increases the likelihood of contamination -- if one of the cows contributing to the pool is sick, or milked without proper attention to sanitation, it can affect a lot of milk. Short Brigade Harvester Boris (talk) 03:27, 12 February 2015 (UTC)


 * That makes a lot of sense and might be true in regards to increase of illnesses due to milk consumption before pasteurization.TMCk (talk) 03:33, 12 February 2015 (UTC)