ACTION OF CYTOST 133 



medium, rendering the latter unfavorable for the con- 

 tinued growth of the organism. In the case of Para- 

 mecium, this has been carefully investigated by Wood- 

 ruff (1911, 1914), who has also demonstrated (1913) 

 that the toxins which are elaborated in mass cultures 

 are more or less species specific, for he finds that 

 media from such cultures, which is incapable of sup- 

 porting further growth of Paramecia, is satisfactory 

 iov tht c\i\\.iY2i\.ioii oi Stylonychia. Robertson (1924), 

 in discussing his experiments with Enchelys, states 

 that "the ultimate cessation of reproduction in old cul- 

 tures is attributable to the accumulation of a product 

 of growth, and possibly of the same product that was 

 originally responsible for the acceleration." This con- 

 clusion of Robertson's is similar to that advanced by 

 the writer (Turck, 1921), to explain the action of 

 cytost on cells of all types. 



In order to obtain cytost from Paramecium, the or- 

 ganisms were grown in large numbers in small dishes 

 for 10 days. The growths were then centrifuged, 

 washed, and dried on a steam bath. The resulting 

 mass was autoclaved with 10 times its weight of water 

 and filtered in precisely the same fashion as that 

 utilized for the extraction of cytost from other tis- 

 sues. In order to ascertain the effects of such cytost 

 upon the growth of Paramecia, six or eight of the 

 latter were transferred from the stock cultures to each 

 of several small tubes containing 1 cc. of water. Some 

 of these tubes were then inoculated with paremecium 

 cytost by adding as much of the dried organisms as 

 could be held on the tip of a platinum needle. 



After twenty-four hours at room temperature, the 

 animals in the tubes containing the cytost were found 



