124 THE ACTION OF THE LIVING CELL 



were not dead, however, for when transplanted to 

 fresh plasma containing a trace of cytost they com- 

 menced to show growth, and after a few transplants 

 in such media they underwent active proliferation and 

 apparently could be carried along in such a medium 

 indefinitely. 



In one instance after the tissues had been grown in 

 plasma plus a trace of cytost for eighteen successive 

 transplants, bits of the tissue were implanted in pure 

 plasma and in the pure cytost extract. In this case the 

 tissues in the latter medium died within two days, 

 while those in the pure plasma remained alive and 

 grew slightly although not so well as cultures made 

 with plasma and a trace of cytost. 



This experience led to an investigation of the ef- 

 fects of higher concentrations of cytost upon tissue 

 cultures. To this end transplants were made from the 

 stock cultures to a medium consisting of two drops of 

 homologous plasma mixed with one drop of homolo- 

 gous cytost. After incubation for 48 hours these trans- 

 plants were found to be dead. This result was obtained 

 a number of times and definitely shows the distinct 

 toxic action of cytost when present in sufficient quan- 

 tity. The lethal effect cannot be attributed to simple 

 dilution of the plasma, for Carrel and Burrows (1911) 

 have shown that a threefold dilution of plasma ac- 

 tually accelerates the growth of tissue cultures. 



Now the interesting question arises : Will heterolo- 

 gous cytost behave in the same manner as the homolo- 

 gous extract? To answer this, the above experiments 

 were repeated, using chicken cytost with human tis- 

 sues and human cytost with chick tissues. Transplants 

 from the stock cultures, originally obtained from the 



