DIRECT AND AFTER EFFECTS OF CHANGES IN 



MEDIUM DURING DIFFERENT PERIODS IN THE 



LIFE HISTORY OF UROLEPTUS MOBILIS. 



I. EFFECTS OF BEEF EXTRACT. 

 LOUISE H. GREGORY. 



In 1905 Woodruff * as a result of his experiments with salt 

 stimulation stated, "the conclusion seems to be justified that a 

 given stimulus produces different effects at different periods in the 

 life cycle." For the past two years while working on the problem 

 of the nutrition of Urolepius mobilis, I have had the opportunity 

 of testing the sensitiveness of the protoplasm of different ages and 

 find that so far as the division rate is concerned, the nature of the 

 response to beef treatment and in all probability to treatment 

 with potassium phosphate and other salts can be predicted if the 

 age of the protoplasm is known. 



The material used in these experiments was taken originally 

 from the stock of Professor Calkins at Columbia, and the same 

 series numbers were kept. From time to time conjugations 

 occurred in the stock cultures at Barnard and new series were 

 started in which case the letter B has been added to the series 

 number to distinguish it from the Columbia series of the same 

 number but possibly not of the same ancestry. In the present 

 paper the results are given of experiments with beet extract only. 

 In a later paper, the experiments with potassium phosphate and 

 other salts will be reported. 



A. THE DIRECT EFFECTS OF BEEF FEEDING. 



Professor Calkins 2 has cultivated Uroleptus mobilis for the past 

 six years on a hay-flour medium, made "by boiling 100 mgs. 

 chopped hay with 130 ings, flour in 100 cc. Great Bear Spring 

 water for ten minutes and diluting this when 24 hours old with 

 equal parts of spring water." Woodruff and Baitsell 3 found that 

 a .025 per cent, solution of Liebig's beef extract was a favorable 

 medium for certain infusoria, and after experimenting with 



solutions of varying strengths, this percentage has been used in 



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