Chapter VI 



THE ORGANISM AND ITS CELLS 



What the Cell-Theory Is, Viewed Historically and 



Substantiiyelfj 



(a) Importance and General Character of the Theory 



THE cell-thcorj seems to some biologists second to the 

 evolution theory alone in its importance to biological 

 science. This may be too high an appraisement ; but beyond 

 question it is and ever will be one of the most influential 

 generalizations yet reached by the science. 



(h) Various Forms of the Theory as Currently Held 



The views of tlie cell incident to our general standpoint 

 necessitate a critical consideration of the theory. What, 

 exactly, is included in it ? Does it contain more than one 

 crucial idea? If so are all equally well grounded in observa- 

 tion? Clearly it has differed considerably in both scope and 

 specific meanings at different times and for different authors. 

 The formulation of it by Theodor Schwann, generally re- 

 garded as its founder, undoubtedl}^ left it open to a con- 

 siderable range of interpretation. Schwann says, "The 

 development of the proposition that there exists one gen- 

 eral principle for the formation of all organic productions, 

 and that this principle is the formation of cells as well as 

 the conclusion which may be drawn from this proposition, 

 may be comprised under the term cell-theory, using it in 

 its more extended signification, while, in a more limited 



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