2IO J. H. WEATHERBY. 



In connection with protozoa Griffiths (1888) made the state- 

 ment, based on his own experiments, that the vacuole performs 

 the function of a kidney, and that its secretions are "capable of 

 yielding microscopic crystals of uric acid." As material for 

 these experiments he used Amoeba, Paramecium, and Vorticella, 

 in mass cultures. In some of the experiments a number of 

 amoebae were placed on a slide and subjected to the murexide 

 test. The development of reddish-purple color indicated the 

 presence of uric acid. In describing these experiments Griffiths 

 says (p. 132): "After the addition of alcohol minute flakes 

 could be distinctly seen floating in the fluid of certain vacuoles. 

 Bearing in mind the murexide reaction, there is every reason to 

 believe that these flakes are nothing more or less than minute 

 crystals of uric acid." These experiments were repeated many 

 times, generally with positive results, indicating the presence of 

 uric acid. At times, however, the vacuole was found not to 

 contain the slightest trace of uric acid. 



Rowland (1924) repeated these experiments using several 

 specimens of Centropryxis and Amceba verrucosa. Cells observed 

 in a dark field immediately after the addition of alcohol did not 

 show the crystals of uric acid in the distended vacuoles, nor did 

 cells after the addition of ammonia show the characteristic 

 murexide reactions, either in the vacuoles or in the culture 

 medium immediately surrounding the organisms. These experi- 

 ments were conducted during a period of five weeks, always with 

 negative results. Paramecia were subjected to the same test, 

 also with negative results. Rowland made use of the Benedict 

 blood-filtrate test for uric acid on cultures of paramecia and 

 amoebae with positive results. The depth of the color developed 

 varied with the age of the cultures, the older ones giving a 

 deeper color. This indicates that uric acid was eliminated in 

 some way by the organisms. 



The question then arises: Is nitrogen excreted by protozoa as 

 ammonia, urea, uric acid, or a combination of these substances? 

 In an effort to answer this question the following experiment was 

 conducted. A large number of paramecia were thoroughly 

 washed, placed in spring water that was free from ammonia 

 and urea, left for a time, and removed by filtration. The 



