134 THE ACTION OF THE LIVING CELL 



to have undergone an increase in number greater than 

 that found in the control tubes to which no cytost had 

 been added. 



When this result had been confirmed several times, 

 the experiment was repeated but the ash obtained by 

 ignition of the dried animals was substituted for the 

 cytost. In water containing traces of such ash the 

 Paremecia were found to multiply more rapidly than 

 in the control tubes, but the increment in number of 

 the control cultures was nowhere nearly so marked as 

 in the previous experiments with the dried animals. 



Since, as is well known, traces of various mineral 

 salts may markedly afifect the behavior of protozoan 

 cultures, it is impossible to state definitely that the ash 

 cytost possesses any specific ability to accelerate the 

 division rate of such organisms. On the other hand, 

 the unashed material, when present in traces, exerts 

 a distinct stimulation of growth as measured by in- 

 creased numbers of organisms. Further, this effect 

 is more or less specific, for when cytost prepared from 

 chicken, rat, or human tissue was substituted for the 

 Paramecium cytost, no such increase in division rate 

 was noted. 



As was found to be the case with tissue cultures, the 

 growth-stimulating principle in the dried ciliates is 

 water-soluble. This was shown in a series of experi- 

 ments in which the 10% extract referred to above was 

 used. Four or five Paramecla were transferred to 

 tubes containing 1 cc. of tap water. A loopful of the 

 cytost solution was added to several of these tubes and 

 the remainder were kept as controls. 



After 48 hours at room temperature, the number of 

 organisms in each of the tubes con\.2i\nmg Paramecium 



