130 THE ACTION OF THE LIVING CELL 



quite uniformly met with failure. Witness for ex- 

 ample the remarks of Harrison (1928) : "It is a very 

 interesting and at present inexplicable fact that single 

 somatic cells isolated in culture media do not prolifer- 

 ate. Experiments to this end in my own laboratory 

 some years ago but not published did not succeed and 

 other workers have reported similar experience. As 

 Fischer put it,"A colony of fibroblasts cannot arise 

 from a single cell even when the nutrient conditions 

 are most favorable. Likewise small groups of cells 

 if isolated do not undergo division and their growth 

 remains at a standstill. On the other hand certain 

 tumor cells (Rous chicken sarcoma) are capable of 

 multiplying and producing colonies when isolated 

 singly." 



It seems, therefore, that in order that a somatic cell 

 may undergo division it must obtain suitable stimu- 

 lants from its neighbors. In this connection, the most 

 careful observations seem to be those of Haberlandt 

 (1919-1922) , who, working with plant tissues, found 

 a direct correlation between the size of the transplant 

 or the number of cells within it, and the frequency of 

 mitoses. In consequence this investigator concluded 

 that some substance arising from the injured cells, 

 which he termed "division hormones," incited the 

 intact cells to division. This is in direct confirmation 

 of the writer's hypothesis — Haberlandt's division hor- 

 mones being synonymous with cytost. 



Similarly, other names have been applied to the 

 growth-stimulating substances present in tissue ex- 

 tracts. They have been termed "trephones" by Carrel 

 (1924), "desmones" by Fischer (1925), and "archu- 

 sia" by Burrows and Johnson (1925). Since, how- 



