98 PROTOZOOLOGY 



tural tubes of Trypanosoma lewisi and Leishmania tropica, the 

 oxygen contained in about 100 c.e. of air of the test tube is used 

 up in about 12 and 6 days respectively. A single Paramecium 

 caudatum is said to consume in one hour at 21°C. from 0.0052 c.c. 

 (Kalmus) to 0.00049 c.c. (Rowland and Bernstein) of oxygen. 

 Amoeba proteus, according to Hulpieu (1930), succumbs slowly 

 when the amount of oxygen in water is less than 0.005 per cent 

 and also in excess, which latter confirms Putter's observation of 

 Spirostomum. The Hypermastigina of the termite are killed, ac- 

 cording to Cleveland, when the host animals are kept in an excess 

 of oxygen. Jahn (1935) found that Chilomonas Paramecium in 

 bacteria-free cultures in heavily buffered peptone-phosphate 

 media at pH 6.0 required for rapid growth carbon dioxide which 

 apparently brings about a favorable intracellular hydrogen-ion 

 concentration. 



Excretion and secretion 



The catabolic waste material composed of w^ater, carbon diox- 

 ide, urea and other nitrogenous compounds, all of which are solu- 

 ble, pass out of the body by diffusion through the surface or by 

 means of the contractile vacuole (p. 73). The protoplasm of the 

 Protozoa is generally considered to possess a molecular make-up 

 which appears to be similar among those living in various habi- 

 tats. In the freshwater Protozoa, the water diffuses through the 

 body surface and so increases the water contents of the body pro- 

 toplasm as to interfere with its normal function. The contractile 

 vacuole, which is invariably present in all freshwater forms, is the 

 means of getting rid of this excess water from the body. On the 

 other hand, marine or endozoic. Protozoa live in isotonic media 

 and there is no excess of water entering the body, hence the con- 

 tractile vacuoles are not found in them. Just exactly why all eucili- 

 ates and suctorians possess the contractile vacuole regardless of 

 habitat, has not been explained. There are accumulating evidences 

 to indicate that the pellicle of the ciliate is impermeable to water 

 and salts, and that the water enters the ciliate body through the 

 cytostome and cytopharynx only. Frisch (1937) observed recently 

 such is the case in Paramecium vmltimicronucleata. If this is true 

 in all ciliates, it is quite easy to understand the universal occur- 

 rence of the contractile vacuole in the cytostome-bearing ciliates. 

 However, it does not explain all cases, as a number of astomous 

 ciliates with a definite peUicle possess contractile vacuoles (p. 488). 



