148 CYTOPLASMIC INCLUSIONS 



ciliate grows during the feeding stages. Persistence and genetic continu- 

 ity is restricted to a few very highly specialized types of vacuoles, and in 

 most cases there is no continuity either in whole or in part. 



The osmiophilic reaction of the differentiated cytoplasm around the 

 contractile vacuoles has given rise to statements that this is a lipoid 

 structure (Nassonov, 1924; VolkonsI<y, 1933; Haye, 1930), and to the 

 interpretation of the vacuolar system as due to the accumulation of 

 lipoids at the vacuole-cytoplasm interface, which is similar to Parat's 

 theory of the Golgi region around the vacuome. It is true that these 

 structures are partially destroyed by lipoid solvents, but such evidence 

 is not to be completely trusted and before acceptance must be corrobo- 

 rated by more specific methods. In Ichthyophthirius these granules are 

 negative to Sudan III and Nile blue sulphate. In Paramecium (unpub- 

 lished work) I have used Ciaccio's long unmasking process and find only 

 a very faint reaction — only slightly more than in the hyaloplasm — and 

 negative results with Nile blue sulphate. These experiments show that 

 there is no concentration of lipoids, either in the excretory granules or 

 in the cytoplasm around the vacuoles. 



The variations in impregnation during the pulsatory cycle and during 

 the life cycle suggest that the osmiophilic reaction is due to some reduc- 

 ing agent (not a lipoid) which is poured into the vacuole during di- 

 astole. The excretory theory of the contractile vacuole is indicated by the 

 name nephridialplasm (Faure-Fremiet, 1925). The similarity between 

 the cytological changes during the pulsatory cycle and in the glandular 

 epithelium or renal tubules has been used in support of this theory (Nas- 

 sanov, 1924, 1925). Further support was given by the demonstration 

 that the osmiophilic granules dissolve in the vacuolar fluid which is then 

 discharged (MacLennan, 1933). In Amoeba the activity of the contrac- 

 tile vacuole is roughly proportional to the number of beta granules 

 around it (Mast and Doyle, 1935b). It is certain in these cases that 

 water plus some other material is being excreted. 



The question, then, is not whether excretion in a broad sense takes 

 place, since water plus dissolved materials is certainly being excreted, 

 but what are the dissolved substances which are carried to the vacuole in 

 granular form? Nitrogenous excretion has often been assumed, but 

 Weatherby (1927, 1929) found that the vacuolar fluid extracted by an 

 application of the microdissection technique showed upon analysis too 



