THE CELL AND PROTOPLASM. 139 



that it is a part of the cell which can not be 

 neglected in the study of the life substance. 

 Again the discovery of the centrosome as a 

 distinct morphological element has still further 

 added to the complexity of the life substance, 

 and proved that neither nucleus nor cell sub- 

 stance can be regarded as the cell or as consti- 

 tuting life. It is true that we may not yet 

 know the source of this centrosome. We do 

 not know whether it is handed down from 

 generation to generation like the nucleus, or 

 whether it can be made anew out of the cell 

 substance in the life of an ordinary cell. But 

 this is not material to its recognition as an 

 organ of importance in the cell activity. Thus 

 the cell proves itself not to be a bit of nuclear 

 matter surrounded by secondary parts, but a 

 community of several perhaps equally important 

 interrelated members. 



Another series of observations weakened the 

 cell doctrine in an entirely different direction. 

 It had been assumed that the body of the multi- 

 cellular animal or plant was made of independent 

 units. Microscopists of a few years ago began to 

 suggest that the cells are in reality not separated 

 from each other, but are all connected by proto- 

 plasmic fibres. In quite a number of different 

 kinds of tissue it has been determined that fine 

 threads of protoplasmic material lead from one 

 cell to another in such a way that the cells are 

 in vital connection. The claim has been made 

 that there is thus a protoplasmic connection be- 

 tween all the cells of the body of the animal, 

 and that thus the animal or plant, instead of 



