PHYSIOLOGY 103 



21°C. from 0.0052 c.c. (Kalmus) to 0.00049 c.c. (Howland and Bern- 

 stein) of oxygen. Amoeba proteus, according to Hiilpieu (1930), suc- 

 cumbs 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 

 on Spirostomum. According to Clark (1942), a normal Amoeba pro- 

 teus consumes 1.4X10~^ mm^ of oxj^gen per hour, while an enucle- 

 ated amoeba only 0.2X10~^ mm.' He suggests that "the oxygen- 

 carriers concerned wdth 70 per cent of the normal respiration of an 

 amoeba are related in some way to the presence of the nucleus." The 

 Hypermastigina of termites are killed, according 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 buf- 

 fered peptone-phosphate media at pH 6.0 required for rapid growth 

 carbon dioxide which apparently brings about a favorable intracel- 

 lular hydrogen-ion concentration. 



Excretion and secretion 



The catabolic waste material composed of water, carbon dioxide, 

 urea and other nitrogenous compounds, all of which are soluble, pass 

 out of the bod}^ by diffusion through the surface or by means of the 

 contractile vacuole (p. 73). The protoplasm of the Protozoa is gen- 

 erally considered to possess a molecular make-up which appears to 

 be similar among those living in various habitats. In the freshwater 

 Protozoa, the water diffuses through the body surface and so in- 

 creases the water content of the body protoplasm as to interfere 

 with its normal function. The contractile vacuole, which is invari- 

 ably present in all freshwater forms, is the means of getting rid of 

 this excess water from the body. On the other hand, marine or para- 

 sitic Protozoa live in nearly isotonic media and there is no excess of 

 water entering the body, hence the contractile vacuoles are not 

 found in them. Just exactly w^hy all euciliates and suctorians possess 

 the contractile vacuole regardless of habitat, has not fully been ex- 

 plained. It is assumed that the pellicle of the ciliate is impermeable to 

 salts and slowly permeable to water (Kitching). If this is true in all 

 ciliates, it is not difficult to understand the universal occurrence of 

 the contractile vacuole in the ciliates and suctorians. 



That the elimination of excess amount of water from the body 

 is one of the functions of the contractile vacuole appears to be be- 

 yond doubt judging from the observations of Zuelzer (1907), Finley 

 (1930) and others, on Amoeba verrucosa which lost gradually its con- 

 tractile vacuole as sodium chloride was added to the water, losing 

 the organella completely in the seawater concentration. Herf (1922) 



