Death and Dissolution of the Organfsm 367 



These experiments show that there is a definite 

 temperature coefficient for the duration of life and that 

 this coefficient is of the order of magnitude of that of 

 a chemical reaction. We are continuing these experi- 

 ments with animals in the presence of food. It should, 

 however, be remembered that the fly carries with it 

 a good deal of reserve material from the larval period. 

 We have carried on simultaneously determinations of 

 the temperature coefficients of the duration of the 

 larval and pupa stage of these organisms at the same 

 temperatures and found ratios similar to those given 

 above for the duration of life with water only. 



7. MetchnikofP has furnished the scientific facts 

 for our understanding of senescence. He has demon- 

 strated that the changes in tissue which give rise tc 

 phenomena of senility are due to the action of phago- 

 cytes. Thus the ganglion cells are altered (digested?) 

 and destroyed by " neuronophags " and this is the 

 main cause of mental senility. Definite phagocytic 

 cells, the osteoclasts, slowly dissolve the bones (by 

 the excretion of an acid?) and this leads to the known 

 fragility of the bones in old age. The whiteness of 

 the hair is due to the action of phagocytes; in the 

 muscles in old age the contractile elements are destroyed 

 by the sarcoplasm, and so on. It agrees with these 

 facts that where organs are absorbed in the embryonic 

 development of an animal, as e. g., the tail of the tad- 



1 Metchnikoff, E., The Prolongation of Life. New York, 1907. 



