622 Lorande Loss Woodruff. 



that the greater dilution produced the largest variation in the 

 fission-rate, except in the MgS04 daily stimulus experiment. 



/J.. Experiments zvith Potassium Bromid. 



The results obtained with potassium bromid in fj^ and y"^ 

 solutions, are plotted in Diagram XII. This shows that KBr in 

 both dilutions had on the whole a very slight accelerating effect 

 on the division-rate, and also that the greatest variation from the 

 control was caused by the -j^-^ solution. The chief effect of KBr, 

 however, seems to have been to change the rhythm of division as 

 shown when plotted in periods of five days. The daily applica- 

 tion of this salt also was deleterious, and I had especial difficulty 

 in maintaining the culture for more than two days when subjected 

 to daily stimulations, which accounts for the omission of the 

 daily curve in three out of the four periods of the experiment. 



5. Comparison of Results. 



Comparing the results of all the experiments with the seven 

 salts when used as initial stimuli, it is clear that K2HPO4 y^Vir 

 caused the greatest acceleration of the division-rate, while NaCl 

 yfo^ produced the greatest slowing of the rate. The largest 

 variation from the control, when plotted in five-day periods, was 

 shown by KCl y"o- All the salts tested agreed in having a 

 marked deleterious effect when employed daily: KjHPO^ y^^ 

 being slightly the most active in this regard. The table on the 

 opposite page gives the actual status of each experiment in relation 

 to the control for each five-day period of the work. 



Calkins tried stimulating his Paramoecium cultures with various 

 salts, among them the dibasic potassium phosphate and found that 

 it not only produced an acceleration of the division-rate, but also 

 that there were less fluctuations in the rate. His results show far 

 more uniformity with this salt than do my own. Greeley ('04) 

 investigated the effects of a number of salts on the physical struc- 

 ture of protoplasm and incidentally on the division-rate of Para- 

 moecium, and he arrived at the general conclusion that "with 

 Paramoecia from alkaline cultures, anions or liquefying agents 

 stimulate cell-division, cathions or coagulating agents inhibit it. 

 Thus I have frequently observed in my experiments that when the 

 liquefying solution is too weak seriously to modify the structure 



