120 PROTOZOOLOGY 



through this avenue is not of a large quantity. How much water is 

 produced during the metabolic activity of the organisms is un- 

 known, but it is considered to be a very small amount (Kitching, 

 1938). The mechanism by which the difference in osmotic pressure 

 can be maintained at the body surface is unknown. It may be, as 

 suggested by Kitching (1934), that the contractile vacuole extrudes 

 water but retains the solutes or some osmotically active substances 

 must be continuously produced within the body. 



Attempts to detect catabolic products in the contractile vacuole, 

 in the body protoplasm or in the culture fluid, were unsuccessful, be- 

 cause of technical difficulties. Weatherby (1927) detected in the 



Fig. 43. Examples of crystals present in Protozoa, a-e, in Paramecium 

 caudatum (Schewiakoff), (a-d, X1000, e, X2600); f, in Amoeba protetis; 

 g, in A. discoides; h-1, in A. dubia (Schaeffer). 



spring water in which he kept a number of thoroughly washed Para- 

 mecium, urea and ammonia after 30-36 hours and supposed that 

 the urea excreted by the organisms gave rise to ammonia. He found 

 also urea in similar experiments with Spirostomum and Didinium 

 (Weatherby, 1929). Doyle and Harding (1937) found Glaucoma ex- 

 creting ammonia, and not urea. Carbon dioxide is obviously ex- 

 creted by the body surface as well as the contractile vacuole. At 

 present the composition of the fluid in the contractile vacuole is not 

 know 7 n. General reference (Weatherby, 1941); permeability of water 

 in Protozoa (Belda, 1942; L0vtrup and Pigon, 1951); physiology of 

 contractile vacuole (Stempell, 1924; Fortner, 1926; Gaw, 1936; 

 Kitching, 1938a). 



Aside from the soluble forms, there often occur in the protozoan 

 body insoluble substances in the forms of crystals and granules of 

 various kinds. Schewiakoff (1894) first noticed that Paramecium 

 often contained crystals (Fig. 43) composed of calcium phosphate, 

 which disappeared completely in 1-2 days when the organisms were 

 starved, and reappeared when food was given. Schewiakoff did not 

 see the extrusion of these crystals, but considered that these crystals 



