DEVELOPMENT 457 



much more rapidly. This is apparently due to their more elaborate 

 nervous systems in part, but chiefly to the fact that when the circulation 

 stops, body-temperature rapidly falls, and this disturbs in many ways 

 the osmotic and chemical metabolism. Even in mammals, however, cer- 

 tain sorts of protoplasmic activity continue a considerable time after the 

 animal as an individual is dead. Thus, the cilia keep up their rhythmic 

 swaying three or four days, and the leukocytes, still more independent, 

 continue their ameboid movements for a week or more, these being still 

 surrounded by their usual nutriment, the plasma. Just in proportion, 

 then, as a cell is immediately dependent on its environment for nutriment, 

 heat, and removal of its waste, does its death closely follow the cessation 

 of the circulation and of the respiration. (See Expt. 51 in the Appendix.) 



Hibernation has to be thought of as a partial cessation of cell-life, for 

 the circulation and respiration (i. e., nutrition) then continue only in a 

 very restricted manner. As we have seen already, human hibernation 

 is sometimes induced voluntarily, as by the fakirs of India. Even 

 normal sleep perhaps is a low degree of this lessening of the general 

 cellular activity of the organism. 



On the other hand, the exact biological status of the dried state in 

 which certain minute animals of our aquaria, notably Tardigrada, can 

 pass, remain months, "or even years," and yet revive readily on being 

 immersed in water, is at present quite unthinkable. It is unlike death 

 as at present defined by biologists, but yet it seems to fail of the death- 

 conditions only in its persistence, the non-decay of its protoplasm, and 

 in its power of recovering the usual activities of life. This state seems to 

 imply that it is only the decomposition of protoplasm, its katabolism 

 unaccompanied by anabolism, that prevents the continuance of life so 

 long as body-decay can be prevented and its protoplasm be still unpoi- 

 soned. But so long as we do not know as yet whether what we call life 

 is a uniform thing, essentially alike from HaeckePs "monera" to man, 

 or whether it may not be of many sorts rather, nothing worth the reading 

 need be speculated in this direction. The phenomena of complete 

 drying followed by revival, however, suggest strongly that in the tardi- 

 grades, etc., at least, the cessation of cell-metabolism may not mean the 

 death of the individual animal. (See Fig. 129, p. 236.) 



The nature of individual-death has already been suggested in the 

 foregoing. It is a less scientific term and a more practical and legal 

 expression. Oftentimes a person thought dead is not so, but very seldom 

 is a person who really is dead supposed alive. On this account the danger 

 is considerable and the means of knowing when an individual is really 

 dead, that is unrevivable, are important, and that too aside from the 

 legal relations of the problem. 



The common law generally recognizes a person as dead when his heart 

 has ceased to beat. As we have seen recently, the heart is about the 

 first organ to begin to move in the fetus, and in Daphnia, for example, 

 on drying up it is the last to die. This presumption that the cessation 

 of the pulse or of the apex-beat is the forerunner of death is a proper 



