Introductory 9 



gle elementary parts only exert an active influence on nu- 

 trition, and the totality of the organism may indeed be a 

 condition, but is not in this view a cause." ^ 



It is hardly necessary to say that Schwann himself 

 adopted the view last presented, and that cells were, as he 

 believed, the "elementary parts" mentioned in his statement. 

 Under other heads we shall find it necessary to speak with 

 some fullness of Schwann's doctrinal views and mode of 

 reasoning. Our needs in this purely historical reference 

 will be satisfied by calling attention to the fact that he 

 states the elementalist theory in general terms only, that is, 

 in terms of "elementary parts" and "molecules." This fact 

 shows his conception of the problem in the large. His con- 

 tention that cells are the elements sought must be under- 

 stood to be an hypothesis secondary only to his broader 

 conceptions. The recognition of this two-fold aspect of 

 Schwann's teaching I deem of prime importance, for it shows 

 clearly that his theory of cells as the ultimate elements of 

 living beings was not a conclusion arrived at by purely in- 

 ductive processes, but rather as an interpretation of cells 

 in accordance with an ancient idea well known to him and 

 adopted by him. So the very great significance of Schwann's 

 work must be looked upon in two distinct lights : first, in 

 that of a generalization of unqualified validity and of the 

 highest importance, concerning the proximate composition 

 of plants and animals, that is, their cellular composition ; 

 and second, in that of furnishing what seemed so solid a 

 foundation for the ages-old elementalist theory of living 

 beings as to secure to it well-nigh complete domination of 

 biological thought for a generation. I think it is not going 

 too far to say that through the influence of the cell theory 

 as promulgated by Schwann, following as it did close upon 

 the foundation of histology by Bichat, the organismal con- 

 ception lay almost wholly dormant during the fifty years 

 from 1840 to 1890. 



