THE CONTRACTILE VACUOLE 425 



in the vacuolar fluid of several forms. Rowland (1924b) was unable to 

 confirm this, but found uric acid in mass cultures of Amoeba and Parame- 

 cium. Weatherby (1929) found urea to be excreted by Paramecium and 

 Spirostomum, but detected no ammonia nor uric acid; ammonia, as well 

 as a questionable trace of uric acid, were found to be excreted by Didi- 

 nium. Specht (1934) found that Spirostomum excretes ammonia, the 

 amount being augmented by lack of oxygen and minimized by abundance 

 of it. Weatherby noticed that cold aqueous extracts of many substances 

 commonly used in culture media (hay, wheat, barley, rye, oats, malted 

 milk, beef extract, blood fibrin, and blood albumen) yield positive tests 

 for uric acid, and suggested this as a possible source of the uric acid 

 found by Rowland in cultures of Para?necium and Atnoeba. Lwoff and 

 Roukhelman (1926) found amino-nitrogen as well as additional nitro- 

 gen, which they report as ammonia plus amide-nitrogen, in pure cultures 

 of Glaucoma. No urea nor uric acid was present. Doyle and Harding 

 ( 1937) analyzed the food (in the form of Pseudo?nonas) supplied Glau- 

 coma, and found that most of the nitrogen present was excreted as am- \ 

 monia approximately six hours after ingestion of food. No urea was V 

 detected. 



If the contractile vacuole is active in excretion of nitrogenous wastes, 

 as is frequently maintained, then one would expect it to be able to ex- 

 crete certain dyes which had been injected into the cytoplasm. Many at- 

 tempts doubtless have been made to demonstrate such a phenomenon, 

 but few accounts of such experiments are to be found in the literature. 

 Apparently negative results have discouraged publication. A personal com- 

 munication from one investigator reports complete failure to demon- 

 strate elimination of dyes by way of the contractile vacuole, although 

 the dyes used in these experiments are known to be excreted readily by 

 the kidney of higher forms. Howland and Pollack (1927) found that 

 picric acid, injected into the cytoplasm of Amoeba dubia, is picked up 

 and excreted by the contractile vacuole. 



Ludwig (1928) studied gaseous metabolism in Paramecium, and 

 found that the amount of oxygen dissolved in water taken with food is 

 insignificant, compared with the respiratory requirement of the organism. 

 For the satisfaction of the oxygen requirement, there must be a quantity 

 of water, saturated with oxygen, equivalent to 260 to 30,000 times the 

 amount taken in through the gullet. Oxygen intake must also occur 



