THE CELL AND PROTOPLASM. 119 



must be together to constitute the life substance. 

 The complicated structure of the cell substance, 

 the decided activity shown by its fibres in the 

 process of cell division, clearly enough indicate 

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

 glected 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 substance 

 can be regarded as the cell or as constituting 

 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 second- 

 ary 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 multicellu- 

 lar 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 between 

 all the cells of the body of the animal, and that 



