212 J. H. WEATHERBY. 



were obtained for ammonia by Nesslerization. In the three in 

 which no ammonia was found the paramecia had been in the 

 water for a period of thirty hours or less. In other experiments 

 in which the length of time was thirty-six hours or more, ammonia 

 was invariably found. This indicates that either ammonia was 

 eliminated in such small amounts that more than thirty hours 

 were required for the concentration to rise sufficiently high to be 

 detected by Nesslerization; or that no ammonia was eliminated 

 as such, the positive test being due to that formed from the 

 hydrolysis of some other excretion product. The latter seems 

 the more probable, for, if ammonia was excreted, the length of 

 time necessary for its concentration to rise sufficiently high to 

 be detected should bear an inverse relation to the number of 

 paramecia per unit volume of water. No relation of this kind 

 was found to exist. The ammonia appeared after thirty to 

 thirty-six hours in all the experiments regardless of the number 

 of animals present. The maximum variation, then, in the length 

 of time necessary for ammonia to make its appearance was 

 twenty per cent., while the variation in the number of paramecia 

 in these same experiments was one hundred per cent, or more. 

 The absence of ammonia in three experiments, and its presence 

 in all the others can be explained if it is assumed that there were 

 too few bacteria present in the three to produce hydrolysis of the 

 more complex excretion products, while in the other experiments 

 there were enough bacteria present. That ammonia can be 

 produced in this way was demonstrated by inoculating a dilute 

 solution of urea with culture fluid. After the solution had been 

 allowed to stand for several hours it gave a positive test for 

 ammonia with Nessler's reagent, indicating that hydrolysis had 

 taken place. 



Many tests were made of the materials used in these experi- 

 ments to prevent the possible introduction of errors. The spring- 

 water was tested for ammonia. The sensitivity of Nessler's 

 reagent was ascertained by finding the greatest dilution possible 

 at which a definite indication of ammonia could be obtained. 

 This dilution was found to be approximately one part in two 

 million. The filter paper on which the paramecia were washed 

 was tested for ammonia. 



