Tom, >>I understand that heart (and some other) tissue(s) can survive for up to two hours without oxygen; whereas, the brain cannot live without oxygen for more than a few minutes. That poses an interesting and very crucial question: When are cells actually considered "dead?" << Answer: there is no good answer to your question, because "death" is a legal term (like "married"), and is not a well defined scientific word, like "mass" or "mammal." It's really more of a subjective judgement. Or perhaps it would be more correct to say that it is a judgement and assertion and prediction: what it means is that the observer is convinced in his/her own mind that the thing will NEVER return to life functions in the future. That is, there is ordinarily in "death" some assertion of **permanence**. Now, of course, you see this causes problems. What's our marker for permanence? Death is not the absence of metabolism, because deep frozen cells do not metabolize, indeed do not do anything at all. But they can be revived. The same goes for mammalian and insect embryos, lower lifeforms like a few simple worms (C. elegans, composed of maybe 936 cells), suitably prepared arthropods like tardegrades, and even one organ from a mammal -- rat intestine has been recovered from liquid nitrogen, and successfully re-implanted to function. So we cannot use the absence of metabolism to guarantee what the future will hold. We may, in fact, eventually learn to revive tissues that seem irreversibly damaged now (by freezing or whatever). Then where will we be? Death is an assertion about the future, but we cannot see the future; therefore it's an idea with a built-in contradiction. To a certain point you may only be as dead as your technology is inadequate. We've seen this kind of thing before with the introduction of CPR (an old technique, BTW). Dualists define death as the moment the immortal stuff leaves the mortal stuff. That sounds nice in the case of a whole human (provided you can tell when that moment occurs, which of course you cannot), but what are we to do with a cell? When a neuron dies, is there anyone who believes that a little neuronal ghost (perhaps shaped like a neuron, but distorted and wispier and with dark eyeholes and an O-shaped mouth going "ooooooo") comes out and ascends to neuron Heaven? No? Then it's a pretty tough question. Pathologists for years have noticed many changes in cells without nutrients, and these have included swelling, mitochondrial swelling, and (later) changes in the character of the nucleus. We used to think that all were evidence of permanence. Wups. It turns out that ischemic heart tissue can show all of the swelling mitochondrial chances and still be recovered with a certain amount of fancy care. You see my point about technology improving and not being sure about the future. Let me propose a better answer (or at least a more materialistic answer) one which cryonicists favor (you know-- those nuts who freeze "bodies"). Life is structural information. It is structure, not function, as shown by frozen things that can be made to run again. Death then is loss of this information. When is the information lost? Hard to say, but it depends on technology. If you wreck your car, you may not be able to fix it. Your car is "dead" to you. But if you take it to a master mechanic and say "fix this," maybe he can. Well, then maybe it wasn't really dead (again the future intrudes retroactively). But if you melt your car into a block of metal and take it to the master mechanic and say "fix this" his first question will be "what is it?" Now the information is gone. See the difference? When you talk about the death of a human, you mean the part that makes us human-- the identity critical brain structures that hold memory, values, abilities, personality traits. These are stored in physical things, like synapses. Information. When is death? When the information is gone. How long after the heart stops is that? A lot more than 5 minutes. At least hours, probably, if electron microscopy is any indication. So the technical resurrection scene in _The Day the Earth Stood Still_, where Klaatu is Jesus ("Mr. Carpenter") and Gort plays mechanical angel, may well occur some day, when technology improves enough. Ditto for quick frozen "dead" people now. They may only be metabolically disadvantaged, flexionally disabled, thermally different, handicapable human beings. The ultimate discriminated against group. If you're interested in some of this, you might want to contact the Alcor Foundation in California (909 736-1703), the major cryonics firm in the country. If you're a writer and are seriously interested in freezing and death, you could do worse than check out the new Sterling Blake novel _Chillers_, just out this month. I vetted that manuscript for medical errors myself. ------------------------------------------------ [Steven] You're entirely correct: its the ice in the intracellular water that does much damage. It can be obviated in some cases by using cryoprotectant chemical to minimize ice formation. Being worked on now are protocols for organs where so much agent is used that no crystals freeze at all, and the whole thing solidif- ies like a glass. Vitrification: the holy grail of cryonics. ------------------------------------------------ [Steven] The key word in your discourse is "irrevocably," since irrevocability to some extend is always knowledge (technology) dependent. Again, see my automobile analogy. When you sequentially damage an automobile by disassembly until finally you have nothing but a pile of unrecognizable bits, at what point does it become "irrevocably" damaged? (the Sorites problem, if you know any philosophy; it applies to both ends of life). Well, certainly while you're stripping your auto you can loose complete function long before you loose enough structure that the informa- tion to make total repair is gone (heck, you loose complete function just when you pull out the coil-distributor wire). I assume the same is true of humans. Consider-- I can rip a phonebook into a thousand pieces, put it all into a trashcan, and stir. Well, my function and organization is now gone to hell. But with enough patience and Scotch tape, I can recover a working book. Death is not just loss of organization, it is loss of enough organization that what WAS can no long be inferred from what IS without (at least) violating any well accepted rules of physics (say, when you burn the scraps to CO2 and H2O). Then only can you have the con- fidence about the future that you need to make the assertion of the presence of "death" NOW. SHow me a cremated guy, or someone who has decayed to a skeliton in a boneyard, and I'll show you a dead guy. Somebody quick frozen in liquid nitrogen? I'm not so sure. There may be a lot of patient guys in the future with a lot of scotch tape. ------------------------------------------------ [Steven] >>Can you tell me what cryoprotectant agent is used? << A bunch of them, mostly glycerol and a few of the odder of the many possible isomers and enantiomers of butanediol. There are also often added lesser amounts of chemicals more toxic (but in different ways), like acetamide and dimethylsulfoxide. Only one lab in the country (in the world, actually) is actively working on whole organ vitrification as of now. It is a Red Cross lab (the Jerome Holland Lab) in Maryland. ------------------------------------------------ [Steven to Steven] >>Steven, I'm unsure of your point. Do you maintain that death is technology dependent, and therefore relative, or that the notion of inability to infer what WAS from what IS, is a non-relative 'test' of death?<< Answer: in a way, both. The ability to infer what WAS from what IS, is technology dependant. If you know you can do it, then you don't have a dead person, even though you may not yet be able to resuscitate at the moment (it's sort of like you just fished a guy out of an icy river with no heartbeat, and can't do anything for him till you get him to a hospital and heartlung machine). If you can't infer what was from what is with your present technology, then you may or may NOT have a dead person, depending. Technology may improve, so you don't know. There are certain clues, however. If you've just burned somebody into a cloud of CO2, H2O and dirty calcium phosphate, then inferring what was from what is will involve getting past uncertainties built into quantum mechanics, and so this seems unlikely. We can never be sure that we won't find ways around currently understood laws of physics (speed of light, backwards time travel, quantum uncertainty, etc.) but this seems a poor bet. If two men are "legally dead," one because of our technical inability to resuscitate at the moment (but with clearly most structural information still present), and the other because of problems with the laws of physics as we understand them (oops, we cremated him), the second is more likely to be Dead with a capital D. Of course, in all of the forgoing I use the word "dead" in its more common context as something which implies permanence, not in its other colloquial context as shorthand for what doctors call more precisely "clinical death" (no blood pressure or respiration), which is (as we all know) sometimes reversible. Sorites is the Greek word for "heap" as in heap of sand, and the sorites paradox revolves around emergent properties of things as gradual changes occur. One sand grain does not make a heap of sand. Two do not. Three do not. But you can iterate this until you get a heap. When exactly does heapness happen? As you add one, then two, then three water molecules, when does wetness happen? You can replace a board on Thesius' ship, and it's still his ship. You can replace two boards. Three. But at some point you've replaced it all, and it's no long Thesius' ship, but a copy. Okay, where do you draw the line? Now there ARE "natural fundamentalist" people with binary views of reality (it is either Thesius's ship or not, period) and sorites is created to bedevil them. Aristotle was in the binary tradition, as are modern Aristotelians like the Randroids and most religious orthodox crazies of all persuasions (I just heard Randall Terry the other night talking about how there were no grey areas of morality). The Binoids are opposed by people who argue probabilistically, like Korzybski and the modern designers of "fuzzy" (as opposed to binary) logic. Why not say it's 60% of Thesius' ship, and forget it? Well, why not is to some extent the Law, which is by nature binary. It's either legal or illegal. And much of law pertains to living citizens. You either have to decide first whether you have one or not. You cannot murder corpses if they aren't citizens, and you cannot murder fetuses if they aren't, either. The problem is that nature does not cooperate, and there is where the abortion wars start (Terry and goons, etc.). To MAKE a human you start with what by analogy would be a very rough blueprint, and a cornerstone. The binary folks insist it is a building. As though a bit of salt and soda and a recipe were a cake. Duh. But that's what happens when you're an Aristotelian. If you argue otherwise in the philosophy of ethics you'll be called a Secular Humanist. Okay, it's a label I wear with distinction, since it shows I have more than two neurons firing. Death is exactly like abortion, except that the Death wars have not yet been fought out legally completely. People do not die all at once, physiologically. "Binary People," who cannot tolerate ambiguity (my definition for a fundamentalist) need an emergent property carrying "essence" which is either there or not there in a person, but this leads to absurdities such as when you resuscitate does the soul go out and into the body like some metaphysical game of paddleball. Yes, if you read the Reader's Digest. But I think not. I think death is sorites. Identity too. Every time Korzybski signed his signature he used to date it, knowing that Korzybski (1) is not Korzybski (2) the next day. There is a wisdom here. Questions? Steve P.S. The difference between a lawyer and a prostitute, it has been said, is that there are some things even a prostitute won't do for money. And you know what one of those things is? A prostitute won't screw you after you're dead.