128 THE ACTION OF THE LIVING CELL 



which are markedly thermostable. Be that as it may, 

 we are at present in complete ignorance of the nature 

 of the growth-promoting substance in cytost, and ash 

 cytost, and must therefore content ourselves with the 

 results of the experiments. 



As was stated towards the beginning of this chapter, 

 various tissues will remain alive for some time but 

 will not grow in Locke's solution. In consequence it 

 became of interest to ascertain whether or not the 

 addition of cytost to such a medium would permit 

 growth to take place. To this end bits of muscle from 

 the thigh and heart of a chick embryo were care- 

 fully washed in Ringer's solution and then implanted 

 in a hanging drop of Locke's solution with the ad- 

 dition of a minute quantity of chicken cytost on the 

 tip of a platinum needle. 



After two days in the incubator these cultures 

 showed very little growth. They were, however, 

 transplanted again to a similar medium, and controls 

 were made in Locke's solution without the addition of 

 cytost. After 48 hours the latter transplants showed 

 practically no growth, while the cultures made in the 

 Locke-cytost medium exhibited a small but distinct 

 growth. 



These cultures were then divided in two, one set 

 being carefully washed in Ringer's solution to remove 

 cytost, and then implanted in Locke's solution; while 

 the second half of the cultures was transferred to the 

 Locke-cytost medium. After two days' incubation, 

 the latter were found to be growing nicely, whereas 

 the former, washed free of cytost, showed but a very 

 meagre growth. Upon again transplanting these cul- 

 tures to their respective media, the cultures made with- 



