174 The Unity of the Organism 



"they had not changed their form, nor had they under- 

 gone any marked changes in structure." This result is the 

 more interesting in that muscle cells of similar sort but 

 contained in a })iece of larva instead of being isolated, con- 

 tinued to differentiate. 



A number of important questions touching the independ- 

 ent life of embryonal muscle cells are awaiting; further study, 

 but enough has been done to leave no doubt that, broadly 

 speaking, they possess a considerable degree of such inde- 

 pendence. 



Not only are cells able to continue their physical activi- 

 ties, but in some cases they are also able to go on with 

 their chemical activities, after being separated from the 

 organism. The evidence is conclusive, then, that once formed, 

 a number of kinds of tissue cells may survive for a long 

 period after removal from the organism and may continue 

 to perform more or less faithfully their wonted activities. 

 Can new cells also be produced under the new and unusual 

 conditions? Undoubtedly. While to a large extent the 

 changes described by all observers in surviving fragments 

 are due to the wandering out and wandering about of cells 

 already in existence, cell multiplication has been clearly 

 seen by too many good experimenters to leave any doubt 

 on the main point. The large increase in mass of the frag- 

 ments described by all those who have 'kept the same cul- 

 tures alive and active for a long time would be conclusive 

 even if cell-division itself had not been seen. 



Carrel and Burrows were apparently the first to witness 

 directly cell division. "A culture contains emigrated as well 

 as proliferated cells. The proliferated elements consist of 

 connective tissue and epithelial cells, the former predomin- 

 ating." ^"^ This is explicit though wanting in detail. But 

 other observers have been sufficiently explicit. As long ago 

 as 1906, H. Deeljen described with considerable particularity 

 the division of the polynucleate leucocytes of human blood 



