The Life-History of Hypotrichous Infusoria. 



617 



twenty-day experiments with the two potassium salts, it is apparent 

 that the dibasic salt had in every case a greater "net effect" than 

 the monobasic salt; and that the more dilute solution of the dibasic 

 salt produced a greater acceleration than the less dilute solution 

 when used as an initial stimulus, and also produced a greater 

 depressing effect when given daily. This is a clear-cut example 



Potassium Phosphate (Monobasic and Dibasic). 

 KjHPO^ KH^PO^ 



100 1250 



3.0 



2.5 



2.0 



1.5 



1.0 



0.5 



0.0 



N 

 1250 



100 



f t t ' 



zftn — hfi m tfi — 



: ' ! 1 ' I ' ----1 : L 



Diagram VIII. 



Effect of initial and daily stimulation with K2HPO4 (y5_ and y ^j^) and KH2PO4 (j5_ and y^^) on 

 the division-rate of Gastrostyla. Averages are for five-day periods. Control (Gastrostyla A, on regular 

 medium) is indicated by a continuous line; initial stimulation, by a broken line; and daily stimulation, 

 by a dotted line. The eight experiments plotted in this diagram were carried on simultaneously from 

 July 6 to July 26, 1904. (C/. text.) 



of a chemical being beneficial in a single small dose but detrimental 

 when used frequently. 



In view of the interesting results with the dibasic salt the 

 K2HPO4 ttVo initial-stimulus culture was continued for some 

 two months after the twenty-day experiment was over. The result 

 of this work is plotted in Diagram IX. From the curve it will be 

 seen that in the sixth period of the experiment the rate fell 



