214 J- H. WEATHERS Y. 



which they were tested for ammonia by Nesslerization. Am- 

 monia was found in the filtrate from every experiment, and 

 generally in higher concentrations than it was in the portions to 

 which no urease had been added. This increased ammonia 

 content after hydrolysis may, then, with a reasonable degree of 

 certainty, be interpreted as indicating that urea from some 

 source had been hydrolyzed with the subsequent production of 

 ammonia. The fact that the three filtrates which gave no 

 indication of ammonia before hydrolysis, gave a distinctly positive 

 test for ammonia after hydrolysis, is alone conclusive in so far 

 as the action of urease is known to be limited to the hydrolysis 

 of urea. Since paramecia were the only organisms present in 

 the water in any considerable numbers, the source of this urea 

 must be attributed to them. It therefore seems evident that in 

 Paramecium at least some of the nitrogen is excreted in the form 

 of urea. 



Is UREA ELIMINATED BY THE CONTRACTILE VACUOLE? 



In an effort to answer this question the xanthydrol precipita- 

 tion test for urea, described by Fosse (1913) and modified to suit 

 conditions of this experiment, was made by injecting the reagent 

 into the vacuoles. The modified reagent consisted of three to 

 five drops of a ten per cent, solution of xanthydrol in methyl 

 alcohol, in I cc. glacial acetic acid. This reagent, in the presence 

 of urea, precipitates long, needle-like crystals of di-xanthyl urea 

 which may be easily recognized. The sensitivity of the modified 

 reagent was found by injecting it, with the aid of the apparatus 

 described above, into a drop of a solution of urea of known 

 concentration. The solution of urea used was successively 

 diluted until the urea content was so low that no precipitate 

 could be observed. It was found that one or more parts of 

 urea in twelve thousand could be detected. The process of 

 injecting the reagent into the drop of solution was observed 

 under a microscope. 



Considerable annoyance was encountered in attempting to 

 inject the contractile vacuole of Paramecium with the xanthydrol 

 reagent in that fumes from the acetic acid in the pipette killed 

 the organism before the injection could be made. This difficulty 



