ACTION OF CYTOST 123 



embryo extract; in higher concentration, it exerts a 

 definitely toxic action, in some instances completely 

 inhibiting growth. (Turck, 1921.) 



For the purposes of these experiments, the tissues 

 were first grown in the usual blood plasma chick em- 

 bryo extracts. In this fashion 34 cultures of chick cells 

 and 25 cultures from a human fetus (about 3 weeks 

 old) were prepared. As needed, transplants were made 

 from these stock cultures to hanging drops of the 

 media under examination. The cytost extract used in 

 the following experiments was prepared by auto- 

 claving 10 grams of autolyzed tissue with 10 cubic 

 centimeters of water. 



Bits of tissue were cut from the outgrowth of the 

 stock cultures and placed momentarily in Ringer's so- 

 lution, which served to wash away the media, and then 

 transferred to a drop of homologous plasma on a cover 

 slip. In the first series of experiments a minute quan- 

 tity of cytost was added to the medium. This was ac- 

 complished by touching the plasma drop with the 

 tip of a platinum needle which had been immersed 

 in the cytost extract. After the cover slips had been 

 sealed onto hollow ground slides, the cultures were in- 

 cubated at 37.5° and transplants to similar media were 

 made every 48 hours. After several days the cultures 

 made in pure plasma showed very little growth, while 

 the same tissues in plasma plus homologous cytost grew 

 very nicely. 



This was not an isolated result, but was duplicated 

 in 308 successive transplants of both human and chick 

 tissues. Hence we may safely conclude that cytost 

 is capable of stimulating cell growth in vitro. The 

 tissue fragments which did not grow in pure plasma 



