128 A. FRANKLIN SHULL AND SONIA LADOFF 



EXPERIMENTS ON THE MECHANISM OF THE PREVENTION OF 



MALE-PRODUCTION 



Osmotic pressure 



The list of substances which effect a reduction in the number 

 of male-producing females includes ammonium salts, sodium 

 hydroxide, beef extract, manure solution, creatin, urea, and 

 some others. In substances of such widely different properties 

 it is difficult to select a common feature to which their com- 

 mon effect upon the life cycle of the rotifers could be attributed. 

 One possibihty that early suggested itself was that the osmotic 

 pressure of the solutions produced the effect observed. Were 

 this the only cause of the reduction in the number of male-pro- 

 ducers, it would be expected that those solutions whose osmotic 

 pressure was the highest would reduce male-production the most. 

 Unfortunately it is probably quite impossible to, say whether a 

 solution produces osmotic effects in living protoplasm unless 

 that protoplasm changes volume. Tables of osmotic pressures 

 are therefore of little value in determining whether, in the ex- 

 periments referred to, the reduction in the number of male- 

 producers was proportional to the osmotic effect of the agent 

 employed. As methods of detecting change of volume of the 

 living rotifers or their tissues were found impracticable, it was 

 necessary to resort to conjecture. In the experiment first to 

 be described, a substance was selected which, if the tissues of 

 the rotifers behaved as theoretically perfect semipermeable 

 membranes, would give an osmotic pressure considerably higher 

 than that which obtained in the other solutions used. The sub- 

 stance selected was cane sugar. 



Experiment 1. Two sisters isolated January 13, 1911, became the 

 parents of the two lines of this experiment, one of which was reared 

 continuously in sugar solution, the other in distilled water. Food 

 and other conditions were the same for both lines. A ^ solution 

 of cane sugar was kept in stock. It was heated daily to prevent fer- 

 mentation, and was tested at intervals for inversion to reducing sugar. 

 Once when Fehling's solution was reduced, the stock solution of sugar 

 was rejected and a new one prepared. This stock solution was diluted 

 to f^ for use in the experiments. 



