THE CELL AND PROTOPLASM. 143 



Organization, in other words, is superior to cell 

 structure, and the cell itself is an organization of 

 smaller units. 



As the result of these various considerations 

 there has been in recent years, something of a 

 reaction against the cell doctrine as formerly 

 held. While the study of cells is still regarded 

 as the key to the interpretation of life pheno- 

 mena, biologists are seeing more and more clearly 

 that they must look deeper than simple cell 

 structure for their explanation of the life pro- 

 cesses. While the study of cells has thrown an 

 immense amount of light upon life, we seem 

 hardly nearer the centre of the problem than we 

 were before the beginning of the series of dis- 

 coveries inaugurated by the formulation of the 

 doctrine of protoplasm. 



FUNDAMENTAL VITAL ACTIVITIES AS LOCATED IN 

 CELLS. 



We are now in position to ask whether our 

 knowledge of cells has aided us in finding an ex- 

 planation of the fundamental vital actions to 

 which, as we have seen, life processes are to be 

 reduced. The four properties of irritability, con- 

 tractibility, assimilation, and reproduction, belong 

 to these vital units the cells, and it is these pro- 

 perties which we are trying to trace to their 

 source as a foundation of vital activity. 



We may first ask whether we have any facts 

 which indicate that any special parts of the cell 

 are associated with any of these fundamental 

 activities. The first fact that stands out clearly 



