402 THE POPULAR SCIENCE MONTHLY. 



energy, integration is also a universal concomitant of vitality, so that 

 for practical purposes life may be provisionally defined as the continu- 

 ous individual integration and differentiation of material energy. 



While these two correlated processes pertain to every variety of 

 life, the physiological expedients by which their respective activities 

 are sustained must vary in conformity with the specific requirements 

 of different structures. A simple unit of protoplasm effects all its 

 vital purposes through direct interchange with its environment, with- 

 out the necessity of any intermediate provision. But, in higher 

 organisms, life is indissolubly associated with certain accessory pro- 

 cesses, and, in these cases, though the molecular interactions on which 

 its essential attributes immediately depend are directly imperceptible, 

 yet it is possible to prove its existence or non-existence by sensibly de- 

 monstrating the presence or absence of these its inseparable concomi- 

 tants. 



Man with his powers unimpaired manifests his vitality in unmis- 

 takable terms, but conditions not incompatible with resuscitation may 

 occur wherein all his functions are so reduced as to be directly imper- 

 ceptible. In such cases, to prevent premature burial, it is important to 

 discover some sign absolutely diagnostic of real or apparent death. 



An essential characteristic of living bodies is their power of actively 

 maintaining a degree of varying integrity of constitution in opposition 

 to destructive influences. This requires the incorporation of extrane- 

 ous materials and their conversion into definite specific structures, and 

 always involves the immediate apposition of ingredients, as well as a 

 reciprocal state of the parts to be nourished. Although such intimate 

 reciprocation of living structures and nutrient materials must always 

 exist, the means whereby it is effected varies exceedingly in different 

 instances. In the lower order of beings it is accomplished very simply, 

 the medium which they inhabit offering directly the requisite pabulum, 

 which their own condition enables them to assimilate without any 

 preparatory elaboration. In more complex organisms a definite cor- 

 relation of parts is necessary to elaborate the crude materials of food, 

 as well as to bring them into immediate relation with the various 

 tissues. 



In some simple forms vital action may be suspended indefinitely by 

 desiccation, being restorable by moisture, and even in some higher 

 cold-blooded animals a state of temporary negation may be induced 

 by congelation, the vital powers returning concurrently with the ab- 

 sorption of heat. In man it is quite different : the animal functions 

 may be suspended, and even some of the organic processes mter- 

 rupted, without extinguishing life, but there are certain of his func- 

 tions the cessation of which for a limited period must inevitably cause 

 death. 



As to their vital significance, man's functions may be classified into 

 essential and supplemental the former including such as can not be 



