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To ascertain whether or not ammonia is present in the lluid 

 of the vacuole, fifteen experiments were conducted in which 

 Nessler's reagent was injected into the organism. The apparatus 

 used in making these injections consisted of the micropipet u 

 developed by Taylor (1925) mounted on the micromanipulator 

 developed by Chambers (1922). The process of injection was 

 performed with the paramecium held by surface tension in a 

 hanging drop of water. The cover-glass bearing the organism 

 formed the top of a cell, the front of which was left open to allow 

 the micropipette entrance. The tip of the pipette was bent up 

 at a right angle to the main shaft to facilitate the injection of 

 the organism suspended on the lower surface of the cover- 

 glass. 



In twelve of the injections the contents of the pipette were 

 discharged into the vacuole. In three the pipette did not 

 penetrate the vacuole, but discharged its contents into the 

 cytoplasm in the immediate vicinity of the vacuole. In every 

 test the reagent, which is highly caustic, caused the immediate 

 solution of the whole organism with the exception of the nucleus, 

 which remained intact for a short time before it too was dissolved. 

 In the three tests in which the pipette did not penetrate the 

 vacuole, the surrounding cytoplasm was dissolved as before, but 

 the membrane around the vacuole remained intact for a short 

 time. After several seconds the membrane was dissolved, causing 

 the contents of the vacuole to be emptied into the solution of 

 Nessler's reagent in which it was floating. In none of these 

 tests was the characteristic straw color observed which, in the 

 presence of Nessler's reagent, indicates ammonia. It seems, then, 

 that if ammonia is present in any part of the organism its con- 

 centration is below the sensitivity of the reagent. All of these 

 experiments seem to indicate then that very little if any of the 

 nitrogen found in the excretion products of Paramecium is 

 excreted in the form of ammonia. 



The test for urea referred to above was made as follows: 

 Urease, a specific enzyme for urea, hydrolyzing it into ammonia 

 and carbon dioxide, w T as added to the portion of the filtrate not 

 used for the test for ammonia in each of the twenty-five experi- 

 ments mentioned. They were then left for several hours, after 



