THE CELL 63 



Columbia University, New York, about the best writer 

 on this subject and shall quote him more than anyone 

 else, to show the reader what we know about the cell at 

 this time. I think he is very careful in his statements, 

 and does not state any propositions as true unless ad- 

 mitted and backed up by very good authority. The fol- 

 lowing is a part of his introduction to the study of the life 

 of the cell : 



"Among the lowest forms at the base of the series are 

 an immense number of microscopic plants and animals, 

 familiar examples of which are the bacteria, diatoms, 

 rhizopods and Infusoria, in which the entire body con- 

 sists of a single cell, of the same general type as those 

 which in the higher multicellular forms are associated to 

 form one organic whole. Structurally, therefore, the 

 multicellular body is in a certain sense comparable with 

 a colony or aggregation of the lower one celled forms. 

 This comparison is not less suggestive to the physiologist 

 than to the morphologist. In the one celled forms all of 

 the vital functions are performed by a single cell. In the 

 multicellular forms, on the other hand, these functions 

 are not equally performed by all the cells, but in varying 

 degree distributed among them, the cells thus falling into 

 physiological groups or tissues, each of which is espe- 

 cially devoted to the performance of a specific function. 

 Thus arises the "physiological division of labor" through 

 which alone the highest development of vital activity 

 becomes possible and thus the cell becomes a unit not 

 merely of structure but also of function. Each bodily 

 function and even the life of the organism as a whole may 

 thus in one sense be regarded as resultant, arising through 

 the integration of a vast number of cell-activities ; and it 

 cannot be adequately investigated without the study of 

 the individual cell activities that lie at its root." 



