DEATH 281 



number of somatic cell-generations," he frankly 

 admits that he is quite unable to indicate the 

 changes in the physical constitution of protoplasm 

 upon which the variations in the capacity for cell- 

 division depend, or the causes which determine the 

 greater or smaller number of cell-generations ; but 

 he urges that if we must wait until we understand 

 the molecular structure of cells before advancing 

 views concerning the nature and limits of their 

 activities we shall probably never solve the 

 problem. " Therefore," he continues, " it is in my 

 opinion an advance if we may assume that length 

 of life is dependent upon the number of generations 

 of somatic cells which can succeed one another in the 

 course of a single life ; and furthermore that this 

 number, as well as the duration of each single cell- 

 generation, is predestined in the germ itself. This 

 view seems to me to derive support from the obvious 

 fact that the duration of each cell-generation, and 

 also the number of generations, undergo con- 

 siderable increase as we pass from the lowest to 

 the highest Metazoa." 



This bold suggestion, based entirely on theo- 

 retical considerations, received striking confirmation 

 a couple of years later, from the results of Maupas' 

 famous researches into the reproduction of Infusoria. 

 The normal mode of reproduction among the ciliated 

 Infusoria is by means of fission, essentially similar 

 to the fission of Amoebae. In addition to this a 

 process of conjugation has long been known to 

 occur in Infusoria, though its real nature has been 

 much disputed. Balbiani described the process in 



