EFFECTS OF CHANGES IN MEDIUM DURING DIF- 

 FERENT PERIODS IN THE LIFE HISTORY OF 

 UROLEPTUS MOB I LI S. 



LOUISE H. GREGORY. 

 2. THE EFFECTS OF DI-SODIUM AND DI-POTASSIUM PHOSPHATE' 



In an earlier paper (i) results of experiments with Uroleptus 

 mobilis were reported which indicate a variation in response to 

 the use of a beef-flour medium according to the age of the proto- 

 plasm. Young and old individuals showed an immediate slowing 

 of their rate of division while mature lines were definitely stimu- 

 lated. With these results at hand it seemed worth while to con- 

 tinue the experiments to see if salts of various kinds would 

 stimulate or depress at different age periods. 



The material and methods used in conducting the experiments 

 have been the same as those of the earlier work and as usual the 

 rate of division is considered an indication of the vitality of the 

 protoplasm. The salts used for experimentation have been di- 

 sodium and di-potassium phosphate. The latter was found to 

 be a stimulant to certain hypotrichs by Woodruff (2) in 1905, 

 and the former caused an increase in the division rate of Para- 

 mecium (3) (Packard, 1926) and Uroleptus (4) (Austin, 1926). 



Two types of experiments have been followed in using these 

 salts, (i) experiments in which the individuals were subjected 

 to an initial dose of the salt for thirty minutes, after which they 

 were transferred to the normal hay-flour medium and treated 

 thereafter in the same way as the control series for the following 

 ten days; (2) experiments in which the salt was added to the 

 normal medium daily in order to insure a constant effect. 



A. THE EFFECTS OF A SINGLE DOSE. 



i . Experiments with Di-potassium Phosphate. 



Sixteen experiments on thirteen different series have been 



conducted. In each experiment the individuals were placed in 



three drops of N/iooo K 2 HPO 4 for thirty minutes and then were 



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