436 SENESCENCE AND REJUVENESCENCE 



More recently Montgomery ('06) advanced a somewhat simi- 

 lar hypothesis. He believed that waste products accumulate in 

 the cells as life continues and that some of them are toxic. Senes- 

 cence and death are the result of the insufficiency of the excretion 

 process. Reproduction is in general an escape or separation of some 

 parts from "an empoisoned mass/' and the part which is thus 

 separated is capable of repeating the life history. But Mont- 

 gomery does not make it clear why the part or parts which separate 

 as reproductive elements do not carry their share of the poisonous 

 substances with them. This is the most important point, for if 

 the reproductive elements do not free themselves from these poisons 

 they, as well as other parts, must die, and there seems to be no 

 reason except a teleological one why parts should separate as repro- 

 ductive elements at all. Here, as in Jickeli's hypothesis, certain 

 cells free themselves, voluntarily as it were, from the poisonous 

 substances which are killing the organism. The chief difference 

 between Jickeli and Montgomery is that for the one rejuvenescence 

 is an excretory process and may occur in somatic as well as in 

 reproductive cells, while the other maintains that only the repro- 

 ductive elements rejuvenate, and that they somehow leave the 

 poisonous substances behind in the body or in a residuum. 



SENESCENCE AS A RESULT OF ORGANIC CONSTITUTION 



Most of those who have considered the problem of age from any 

 general viewpoint have maintained that the conditions which 

 determine senescence and death are found in the physiological 

 constitution of the organism. Seventy years ago Johannes Muller 

 ('44) expressed this opinion; some forty years later Cohnheim ('82) 

 took the same position, and in more recent years this view has found 

 numerous supporters. 



Butschli's suggestion ('82) that death is due to the exhaustion 

 of the supply of a certain substance the "life ferment" which is 

 gradually used up during life, and that the protozoa and the germ 

 cells of multicellular forms do not die because they are capable of 

 producing the substance anew, is not much more than a statement 

 that death is the result of life without rejuvenescence. Cholod- 

 kowsky ('82), on the other hand, suggested that death was rather 



