216 J. H. WEATHERBY. 



Maupas, the volume of water evacuated by a definite number 

 of paramecia in a definite period of time was calculated. From 

 this the concentration of urea that would be in the fluid of the 

 vacuole, if its function is excretory, was computed. The results 

 of these calculations show that the concentration of urea in the 

 fluid of the vacuole would have to be of the order of one part in 

 two or three thousand to eliminate through it the calculated 

 amount of urea. 



The reagent injected into the vacuole is, as previously stated, 

 sensitive to one part of urea in twelve thousand. Since there 

 was in these injections no indication of the presence of urea, 

 it is evident that the results of these experiments are in opposition 

 to the theory that the vacuole is an organelle whose function is 

 the removal of the nitrogenous waste products of metabolism, 

 unless it functions specifically in eliminating uric acid, which 

 is not probable. If, then, it is true that the contractile vacuole 

 functions either as an excretory organelle or a mechanism for 

 regulating the hydrostatic pressure within the cell, it is evident 

 that the results support the latter. 



SUMMARY 



1. The presence of ammonia and urea in Paramecium cultures 

 has been demonstrated. 



2. Ammonia is due to the hydrolysis of urea, and is not 

 excreted as such. 



3. Nitrogen is eliminated in the form of urea. 



4. All the urea excreted can not be eliminated through the 

 vacuole. 



5. The function of the vacuole is not the elimination of 

 nitrogenous waste products of metabolism, but is probably the 

 regulation of the hydrostatic pressure within the cell. 



BIBLIOGRAPHY. 

 Butschli, O. 



1887-89 Die contraction Vacuolen. Bronn's Thier-reich, Protozoa, Bd. I, 



S. 1411-1459. 

 Calkins, G. N. 



1901 The Protozoa. New York. 347 pp. 

 1909 Protozoology. New York. 349 pp. 



