Wikipedia:Reference desk/Archives/Science/2015 July 15

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July 15

bainbridge reflex

wanna know about bainbridge reflex05:52, 15 July 2015 (UTC) — Preceding unsigned comment added by 36.252.1.148 (talk)

Have you tried Bainbridge reflex? Richard Avery (talk) 06:14, 15 July 2015 (UTC)

Mononucleosis

Is kissing the only way mononucleosis is transmitted? 90.192.122.101 (talk) 07:34, 15 July 2015 (UTC)

And sexual intercourse. As the article says, "A person becomes infected with this virus by direct contact with infected body fluids", including saliva, urine, blood, and tears, so any licking and spitting would do it, and sharing food etc.--Shantavira|^{feed me} 08:01, 15 July 2015 (UTC)

then why isn't it more common if it can be pretty much transmitted through all of those? That's almost daily human contact. Surely everyone should get it then. 90.192.122.101 (talk) 09:04, 15 July 2015 (UTC)

Our article says, "About 95% of the population has been exposed to this virus by the age of 40, but only 15–20% of teenagers and about 40% of exposed adults actually become infected." You're correct that almost everyone gets it eventually. The terminology can be a little confusing. Let me try to summarize. Mononucleosis has multiple causes, but the overwhelming majority of cases are caused by the Epstein–Barr virus. However, only a minority of people who contract the virus will develop mononucleosis. In the majority of people it causes no or only minor symptoms. Epstein–Barr is a member of the Herpesviridae, which also includes among other viruses the chicken pox virus and the viruses that cause herpes simplex (usually simply called "herpes"). The Herpesviridae are adapted to evade the immune system and establish a latent infection that persists for the rest of your life, essentially "hiding" inside some of your cells. The viruses sometimes simply lay dormant indefinitely, but they can become reactivated and cause a new outbreak. Herpes is well known for repeated cycles of active and latent infection, and reactivation of the dormant varicella (chicken pox) virus in previously infected persons is what causes herpes zoster, commonly known as shingles. Because they usually persist indefinitely in infected hosts, cause relatively limited symptoms, and are easily transmitted, many of the Herpesviridae are near-universal in the adult human population. This ties into what's called optimal virulence; pathogens tend to become less damaging to their hosts over time. Pathogens want to reproduce, and relatively healthy hosts can spread them better than really sick or dead ones. These viruses are quite evolutionarily successful! As a personal demonstration, I am cytomegalovirus positive, but I've never had anything worse than a typical cold, so I probably had an asymptomatic infection. The only reason I know I'm infected with the virus is because I donate blood, and all donors are tested for the virus, because CMV positive blood can't be given to pregnant women, newborns, or immunocompromised people. Anyway, I hope that was informative! If you liked my explanation, I have one request: donate blood regularly if possible! It saves lives! Thank you. --108.38.204.15 (talk) 12:26, 15 July 2015 (UTC)

Look at virulence and optimal virulence. Diseases do best the longer their hosts live and the better those hosts spread their germs to others. New pathogens like HIV usually spread at first because they are highly communicable. But if they cause quick morbidity and death, they don't pass on to as many hosts as possible. Over time, strains that stress the host the least tend to become the most common (although their are other factors involved which can counteract this). Many viruses like herpes viruses ("everyone has herpes") become widespread but cause fewer obvious symptoms. For example, my mother gets cold sores, but none of the rest of us in my immediate family do. I got shingles while in the hospital, but the case was so mild I thought I had a mosquito bite. Of my clique at college, only one of us "got" mono (i.e., symptoms), and that led to hospitalization for jaundice, but none of the rest of us did, although there was some intimate contact within the group. As long as a disease has any easy time of spreading (promiscuity, large classrooms) it will tend to become less and less symptomatic while it becomes ever more prevalent. μηδείς (talk) 21:13, 15 July 2015 (UTC)

Saved shark? Looked pretty dead to me.

There've been some reports (for example here) of a stranded juvenile great white that was supposedly "saved" yesterday in Cape Cod. In the footage that I've seen it looked utterly dead and I have not seen any footage showing it swimming away. Does it look like websites just repeated the story without checking it? How do they know it was saved? Does anyone here have any source that can prove it swam away? Is it at all credible that a shark that was beached for hours can survive the ordeal? Contact Basemetal here 14:28, 15 July 2015 (UTC)

Did you not see it move its mouth and tail at ~5 seconds, and everybody cheers? Later, in the water, a guy says something like "see the gills pumping"? and if you look closely you can see that too. The shark certainly doesn't look dead to me in that video, though I admit it's not clear or certain that it will still be alive next week (I guess that goes for all of us ;) For further video evidence, see here [1] - the second video shows the shark clearly swimming under its own power - apparently they dragged it about a mile out. Probably took a while to recover from the shock and get more oxygen in to its blood. SemanticMantis (talk) 14:47, 15 July 2015 (UTC)

I did see it move at the beginning but then by the time they towed it into the water it looked pretty dead. But you're probably right. Here's another video. It seems to show footage of the shark finally moving in the water and it confirms that it took a long time to bring it back. Now as to my more general question: How long can a shark stay out of the water and still remain capable of being brought back? Incidentally this reminds me of a scene (having to do not with a shark but an octopus) in the Japanese movie Departures (about 18 m 30 s into the movie) where the woman (Ryōko Hirosue) brings home an octopus for dinner. But then suddenly the octopus starts moving on the kitchen floor. The couple (husband played by Masahiro Motoki) rush to release it in Tokyo harbor but the guy's already dead. How long can you keep an octopus out of the water before it dies for good? Contact Basemetal here 18:06, 15 July 2015 (UTC)

See here [2] for a discussion of the octopods. Several people are reporting survival out of water times on the scale of hours. Given that many of them have a natural behavior of moving over land between tide pools, it's not so surprising that they can survive out of water for a while, especially if kept moist. SemanticMantis (talk) 18:43, 15 July 2015 (UTC)

Maybe this will turn out to be like the lion and the mouse, and the shark will refrain from munching on swimmers. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:01, 15 July 2015 (UTC)

Yeah right I wouldn't count on it. Now if you wanna get in the water, be my guest A shark's brain is pretty small. They're superefficient killing machines but I doubt they can remember anything. Killer whales would be better candidates, but they don't munch on swimmers to begin with. At least there's no recorded case in the wild and what happened in Florida a few years back was clearly an accident. (In fact the guy didn't munch on anything but it did drown its trainer) Contact Basemetal here 18:06, 15 July 2015 (UTC)

"At least there's no recorded case in the wild" - in other words, they make sure not to leave any witnesses. Iapetus (talk) 10:45, 16 July 2015 (UTC)

Without getting into the realm of legal advice, it's still interesting to imagine that if someone is attacked by a shark, and it could be proven to be the one that was put back in the ocean, whether those who did so could be held liable for the attack. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:27, 15 July 2015 (UTC)

There should be a big "if" attached to the "it could be proven". I'm not sure anyone took a DNA sample that would stack up in court, nor did anyone attach a tracker. It's possible there are sufficient high resolution photos showing the dorsal fin or other unique markings, and despite these being from a juvenile [3] [4] they could be used to uniquely identify the shark later (bearing in mind the standards acceptable for tracking are likely to be different from that for a court case) but this seems unlikely. Noting you'll also need to be able to use the same method for the attacking shark. Nil Einne (talk) 02:55, 16 July 2015 (UTC)

If you tie a rope around a shark's tail, and drag it into the ocean with a boat as these people did, how then do you get the rope off the tail?Edison (talk) 03:13, 16 July 2015 (UTC)

Using hands? Maybe a knife or safety scissors. I can't tell from the video how they tied it on, but I'd probably use some sort of quick release knot, perhaps some variant of the Highwayman's_hitch [5] or some other slipped knot. SemanticMantis (talk) 14:20, 16 July 2015 (UTC)

From comments I've seen the bystanders could have dragged it into the water with their bare hands (assuming they had the physical strength to do it) with no danger to themselves as the shark in the position it was beached in couldn't hurt them (unless they were foolish enough to go stick their hands in its mouth) but that alone would have been pretty pointless as the real hard thing was to induce it to start breathing again, to restart its gills. Apparently, even in the water, if a shark doesn't keep moving, it suffocates. Other species of fish have the ability to breathe while staying put but not sharks. So, after they had dragged it into the water, the shark had to be towed alongside the boat to revive it and that took some time. In any case you couldn't do that by dragging it from its tail. They had to tie a rope around its trunk or whatever that part of the body is called. I suppose that makes the problem of getting back your rope a little easier to solve, if that's what you're worried about. Contact Basemetal here 15:41, 16 July 2015 (UTC)