Studies on the Life History of Protozoa. 431 



A. Potassium Salts. 



a. K^HPO^. On the 8th of June, 1902, one individual from 

 the line of A2 was treated for 30 minutes with a solution of dibasic 

 phosphate of the strength of one drop of ^^^n to six drops of usual 

 hay infusion. The result was a marked increase in the rate of 

 division for a considerable period as compared with the control 

 series, as follows: 



Average daily division-rate for 5-day periods, June 8-July 5. 



Stimulated Aj. Control Series. 



1st Period 8 8 



2d *' 8 6 



3d " 8 6 



4th " i.o 2 



5th " 1.6 o 



On the 27th of June the above experimental series was 

 substituted in the regular culture series and the descendants 

 of these individuals formed the regular lines until the final 

 extinction, subject, of course, to the other experiments as stated 

 elsewhere. 



A stronger solution (1-5) and for a longer period (i hour) was 

 used with A3 on June 26. The individual died in three hours. 

 On August 2 1 the same strength was used, but for only 25 minutes; 

 the individual died in four days without dividing. The general 

 effect of this salt was, therefore, favorable, with evidence that a 

 certain optimum strength is alone beneficial. The beneficial effects 

 upon the endoplasmic structure are shown in Figs, il and 13. 



b. KH^PO^. Experiments with the monobasic salt were also 

 made and various proportions were used, but none was successful. 



c. KCN. Various proportions of "0 of this salt were used, the 

 most successful being one drop of the solution to twelve drops of 

 hay infusion. This was not strong enough to kill the bacteria 

 which afford the only food for Paramcecium. Four individuals 

 were immersed October 29 in the mixture and left for 24 hours. At 

 the end of this time each had divided once, while none of the con- 

 trol series had divided. Of the eight individuals resulting from 

 this treatment, four were placed again in the KCN solution, 



