1 6 SENESCENCE AND REJUVENESCENCE 



investigation, for as soon as we attempt to determine how it differs 

 from dead substance death occurs. 



Moreover, if death results from change from extreme labihty 

 to relatively high stability we should expect at least many of the 

 proteids of the body to undergo marked changes in appearance and 

 physical properties at the time of death. Some changes of this 

 sort, such as coagulation, do occur, but coagulation does not neces- 

 sarily involve chemical transformation, and in general the visible 

 changes in the proteids with death are not very great. Certainly 

 they are not as great as would be expected if such a profound 

 chemical change occurs. 



If the energy of the organism is due to the explosive trans- 

 formation of highly labile molecules into more stable conditions 

 and if death also results from a more extreme change of the same 

 sort in the substance of the organism, we should expect to find a 

 very large amount of energy developed at the time of death. If 

 all the living substance changes into dead substance in the course 

 of a few moments or a few hours, or even a few days, what becomes 

 of the energy liberated ? The amount of energy developed by such 

 a change would necessarily be greater than that resulting from the 

 most extreme stimulation which did not kill, for such stimulations 

 are supposed always to leave some part of the hypothetical living 

 substance intact. Such a liberation of energy could scarcely fail 

 to produce profound changes of some sort, either mechanical, 

 electrical, or thermic, but death is not necessarily accompanied by 

 any energetic changes of such magnitude as might be expected to 

 occur according to the hypothesis. 



How, we must also ask, are we to account for growth on this 

 basis ? What peculiar property of the living substance determines 

 not only that the molecules which break down shall again be built 

 up or replaced, but that other new molecules shall be added? 

 Various highly hypothetical answers have been given to this ques- 

 tion, but the fact remains that so far as we know no similar process 

 exists elsewhere in the world. The growth of crystals has often 

 been compared with that of organisms, but the resemblance is at 

 best only very remote, for growth in the organism is certainly closely 

 associated with chemical reaction of a complex character, while in 

 the crystal it results from a physical relation between like molecules. 



