Friday, May 25, 2012

Butt scratching, finger sniffing

Could it be a way of human auto-evaluation of the olfactory system-detectable free-radicals that eminate from fecal matter?

Friday, May 18, 2012

P values

Warning! This is an extremely boring post about statistics, and is mostly for my own use. Feel free to ignore this post!   

As I continue to study statistics, I'd like to write out and better internalize a few reminders about one of the most ubiquitous features of a statistical test: the p-value (also written as P-value or p or P).  Every time I think I finally have this concept nailed I realize I forgot a detail somewhere.

The p-value is the probability of getting a more extreme result if we assume that the null hypothesis is true. But for the p-value to be of any use, a somewhat arbitrary cut-off level needs to be established before the test, usually at 0.05.

For example, 100 rats are injected with a drug. For the injected rats, mean response time to a stimulus is 1.2 seconds, with a standard deviation of 0.5 seconds (and the distribution is normal). Rats not injected have a mean response time of 1.05 seconds. The null hypotheses in this case would be that the drug has no effect. So what we want to know is how many standard deviations away from 1.05 is 1.2 in this test distribution? Simply put, what is the Z-score? Well, 1.2-1.05 equals .15, and since we want this difference in terms of standard deviations we divide by 0.5 (which was given above). This equals 3. From the 68/95/99.7 rule we know that a result that is 3 standard deviations away from the Ho mean has a probability of (1-0.997) = 0.003 = p-value.

OK, I wrote all that to say what this p-value of 0.003 means (and what it doesn't mean). Since we decided beforehand that an acceptable alpha (risk of rejecting the null hypothesis when in reality it's true) is 0.05, we can reject the null hypothesis. This doesn't mean that the alternative hypothesis is necessarily true! It just means that the effect found in this sample for this particular experiment probably did not happen by chance alone. That's all.

Another important thing to remember is that a low p-value alone doesn't indicate the strength of a correlation. For example say that I did two tests to test the effectiveness of two drugs, and the drug A test had a p-value of 0.001 and that drug B had a p-value of .04. I can't say that drug A is more effective, since maybe the drug B test had a larger sample size. P-values are can change suddenly when the sample size is small - for example, flipping a coin 20 times and getting 14 heads is statistically insignificant, but throwing 15 heads gives a p-value of less than 0.05.

You can't compare p-values across experiments. It's an indicator that is proper to that experiment alone.

Deciding which alpha level to use and how to interpret the p-value is dependant on your a priori knowlege of the subject, and your confidence in the efficacy of your test (is the sample good, are all the important variables accounted for, etc.) P-values are not magic numbers that prove hypotheses!

Tuesday, May 15, 2012 

Cool blog with stunning pictures of the sun.

Last day of autopsies

Last week I had one final day of autopsies.  In the morning we saw an obese, diabetic, and quite hirsute black woman and the near-completely decomposed remains of a man.  It was hard to ignore the loads of hair on the woman's butt and her stubbled chin - just another reminder of human variability!  The brain was extracted, and I sidled up next to the intern to see what she would find.  The arteries were extremely hardened and congested.  After her findings were recorded I was allowed to poke around with a scalpel.  I was happy to have the chance to get the feel of everything.  Sure, you can read that the brain weighs 1000-1700 grams, but holding in your hands is much better!

Next we looked at the heart, which presented severe atherosclerosis, the calcified fatty accumulation in the coronary arteries.  There was also a spot that had ruptured. In the area around the heart, large amounts of "agonie" was found (that's to say gelatinous globs of coagulated blood).  The diagnosis was clear - she suffered from intense hypertension and her heart literally burst as a result of extremely high blood pressure.

Next was a body that was exhumed from somewhere.  Unfortunately I didn't quite understand the parsimonious backstory I was told.  All I can say is that it was at least 6 months old and didn't stink! *EDIT: The body was more than 3 years old.*  The head and upper torso were completely desiccated, but interestingly the butt and legs had maintained their shape more or less.  This is because under the right environmental conditions high concentrations of fat can turn into a waxy, soapy substance.  Essentially the outside of the bottom half of the body had turned into soap, preserving everything within.

A clean-cut doctor I had not met before was in charge of the operation.  He paid little heed to the lackeys that surrounded him, giving orders left and right.  He suddenly put me in charge of labelling all of the little plastic containers that we put the organs in, which I was more than happy to do!  Of course I was the least qualified person in the room for that, since I don't always know how to spell the French anatomical vocabulary.  It was sort of embarrassing, but I managed!

 In the afternoon we saw the autopsy of easily the most healthy-looking person we saw.  He was a man in his 40's, quite athletic - almost pure muscle, but not in a gross way.  The story was that he went out for a jog and just never came back.  His wife called the police three days after!  Maybe he just disappeared like that in the past.  He had a history of heart problems, and we found a coronary stent when we cut open the heart.

His liver was huge - 2300 grams. The doc explained that when the heart isn't circulating enough blood, the liver needs to compensate.  I didn't quite understand...  I'll look into it.  

Saturday, May 5, 2012

Putrified Corpses

I told you about Wednesday and Friday (though I know I left out a lot of details) but I didn't tell you about Thursday.  This is partially because I was searching for the proper adjectives to describe the smell of a putrified corpse.  Most of us have encountered rotting meat, but usually in small quantities, and once the evil is found, it is quickly disposed of. I hope that none of you has to endure what I endured for an hour and a half.

The problem with attending the autopsy of a decaying body is that it only gets worse.  There's no plateau to the smell.  The room stinks when the body is still in the bag.  It's worse when the bag is opened.  Another wave of putrescence hits you when the skull is opened, and the brownish-black smoothie of a brain the plops out.  Just when you think the odor can't be any worse, they open the thoracic cavity.  After they remove the rotten liver and lungs, you think, OK, I can deal with this.  Then they pull out the rotten colon and the weeks old feces within.  That's when I excused myself for a breath of fresh air.

I'm also in the embarrassing situation of not having much to say about the autopsy itself.  I was so distracted by the odor that I didn't really pay attention to what was going on.  There didn't seem to be anything going on.  I think it was just an old guy who died in his house and it took a while for anyone to find him.

One thing I didn't know is that putrification causes the testicles to swell up.  The penis was not visible because the testicles had ballooned from the gasses and fluids that accumulate.  His face was purple because  he had been lying face down, so all the blood pooled there.  This is called lividity.

I left early and took the afternoon off.  There was just another putrefied corpse that afternoon, and I just didn't see the purpose of subjecting myself to that again.  I can handle visual horror, but olfactory horror is too much.  I couldn't even eat lunch because the smell was stuck in my sinuses.  The beautiful sandwich that Audrey had made me tasted like two-week-old man.

I don't know how these doctors do it.  There's no secret to it - their faces all showed signs of extreme discomfort.  It's a living.

Friday, May 4, 2012

In the thin and thick of it.

 This morning I saw the autopsies of two women.  The first seemed to be a case of tuberculous anorexia, and the second a knife-induced intrapericardial hemorrhage.  The extremely skinny woman was initially thought to have died from complications due to her anorexia, but when we opened her lungs we found that they were riddled with infection.  The chain-smoking doc immediately said "TB."  I took a step back.  Another doc was called down to confirm and she wasn't so sure.  Infection, yes, but she said TB has a "chalkier" look - less wet looking.  At any rate, I was assured that it was no longer contagious.  Nonetheless, all of the interns put on masks.  The fact that her lungs were in such horrible shape and that she never went to the doctor because of her assuredly nasty cough means that she was in a pretty 'irregular' situation as they say.  Probably homeless.  The doctor said she was psychotic.

The next woman was much healthier looking.  The room buzzed with the possibility that she was pregnant.  She looked it.  She had several superficial cuts on her chest.  The wounds didn't even reach the muscle.  But when she was flipped over there was a knife sticking out of her back!  The handle had been removed by the police to ease transportation, but the blade was immovable.  It was stuck in a vertebra and a rib, but which ones?

"Ho!  Les anthropologues!  Vous devriez savoir.  C'est quelle côte?" chain-smokey asked us.  (Côte = rib.)  I immediately replied, "Ah, c'est évident, c'est la cinquième" with a facetious grin, thinking that it was near impossible to know before cutting her open.  But nobody laughed!  The doc checked the x-ray.  "Ouaip!  C'est en effet la cinquième côte!"  I explained that I had been joking, but my colleagues just looked at me with suspicion. 

As the autopsy proceeded, large dark red gelatenous globs were found near the heart where the knife had touched the heart.  The doctor held the globs before me and said, "Tu sais qu'est-ce que c'est?  Thees eez euh... agonie.  Comment dit-on 'agonie' en anglais?"  "Agony," I said.  When you die your blood stops coagulating.  Large amounts of coagulated blood means that she died slowly.

Finally we cut open her uterus and found not a baby but a sterilet (intrauterine device).  She was just fat!

Wednesday, May 2, 2012

Pop Pop Pop, Watchin' Motha Fuckas Drop!

At lunch I ordered 'steak frites' but the smell of the burnt man would not leave my sinuses.  The steak tasted like a Marseille BBQ!  I filled up on fries.

On the way to the autopsy room the professor started talking about how the man we were going see was a known drug dealer, and that we shouldn't feel too bad for him.  It's not like he was a innocent caught in the cross-fire.  We should think of it as a "work accident" (accident de travail).

Let me tell you, an AK will fuck your shit up.  The guy was hit maybe 10 times in the chest and head.  There was hardly any of his brain left.  The ever-hilarious chain-smoking doctor opened up the cranium for all to see the paltry remains and said "See the size of an average gangster's brain?  100 grams!"  (An average human brain is 1300 grams.)

We got to take a more active role in this autopsy, helping carry stuff and getting to fiddle with his innards.  The doctor urged me to pick up an arm to see how hard it is to move a stiff.  I did, and the corpse grabbed me!  I didn't shriek like a little girl, but almost.  I moved the wrist in such a way that the tendons naturally caused the hand to grip me.

I also handled and examined his heart, lungs, stomach, liver, pancreas, and spleen.

They very carefully examined each entrance and exit wound to determine how many bullets hit him.  They longly debated whether or not a bullet had shattered midway causing two exit wounds.  They smoked and debated some more.  Voices were raised, sarcastic volleys followed.  There was an uneasy balance between the fact that it was pretty obvious what happened here (he was a drug dealer whose head was shot to hell by other drug dealers and that's how he died, duh) and the fact that for legal purposes they needed to be fairly precise.

On the train ride home I probably passed within a few hundred meters of the site of the shooting, near St. Joseph.  Quite an odd feeling stopping at St. Joseph and seeing all the housing projects and all the poor people who inhabit them.  I don't know if I would have ended up any differently than the guy whose spleen I played with if I lived there.  Precisely 24 hours ago, he was probably driving around like everyone else, alive.  I'm sure he was ignorant, and brutish and whatever else you want, but I cannot feel better or worse about his death than that of the 70 year old woman who died of complications in the hospital.

I've seen some shit

This morning I finally had the famous autopsy experience everyone has been talking about since September. After so much time wondering what it would look like, smell like, feel like, I now have the answers!  After a brief tour of the facilities, us four students and the professor donned our smocks and shoe covers and entered the autopsy room.  It's a modest space with plenty of sunlight, with two stainless steel autopsy tables on either side of the room.  There was an elderly woman on the table to the right, and a black body bag on the left.  A few gendarmes were hanging out in the observation area, because the guy in the body bag is the result of a criminal affair.  Then before I could really get my bearings the room burst into activity, with two teams of five starting to work on both cadavres.

The first shock was when they opened the body bag.  The guy was almost entirely carbonized.  He was a victim of a barbecue marseillais - he was killed execution-style with a handgun, then placed in a car, doused in petrol, and set ablaze in order to obfuscate any evidence.  It smelled like, well, burnt meat! As they started slicing him up his flesh really looked like a well cooked steak.  The chain-smoking head doctor was compelled to cry out, "Regardez!  Il est à point!" (Roughly 'Look!  He's cooked to perfection!').  The ambiance was anything but somber.  They do this day in and day out. 

On the other side of the room the autopsy proceeded more normally, with the systematic removal and inspection of all the major organs.  First the brain was extracted, which was one of the smellier operations, not because the brain smelled, but because the friction from cutting bone with a small circular saw caused a burning odor.  Otherwise the room did not stink.  The old lady had died only an hour or two earlier, and was therefore 'fresh' and the barbecue guy just smelled like left-over steak.  Once they removed the bowels though, everyone caught a good whiff of dead people poop.

At the end, the friendly, overtly gay technician was left alone to whistle and sew up the old woman to make her more or less presentable for her funeral. He took good care to keep her hair in order.

This afternoon we're going to see the autopsy of a guy who was driving along last night (not far from my school) when another car pulled up and blasted him with a Kalachnikov.  I'm 'lucky' since gang related killings have been relatively infrequent lately.  There have been about a dozen since the beginning of the year, and I get to see two in one week!

Tuesday, May 1, 2012

I hope I am

Recently I've been having this recurring feeling that I might be somehow mentally deficient, and that everyone around me is just humoring me. I say it's a feeling because I really feel it in my bones when it happens - it's almost spine-tingling as I entertain is as a real possibility. I could be an idiot after all. Idiots rarely recognise themselves as such.

A Report on Idiots in Massachusetts (1848)