PHYSIOLOGY 93 



mastigina. A similar relationship seems to exist between Paramecium 

 hursaria and a zoochlorella, Paraeuplotes tortugensis and a zooxanthella 

 and others (p. 25). Pringsheim showed that organic matters from 

 zoochlorellae are passed on to their host, Paramecium hursaria, 

 to be used as food. Through studies of relationships between 

 zooxanthellae and invertebrates Yonge observed that the zooxan- 

 thellae utilize carbon dioxide, nitrogen and phosphorus which are 

 the cataboHc products of the host and supply in return oxygen, fats 

 and carbohydrates to the host. 



Saprozoic (saprophytic) nutrition. In this nutrition, the Protozoa 

 obtain nourishment by diffusion through the body surface. This is 

 accomplished without any special organellae. Perhaps the only in- 

 stance in which the saprozoic nutrition is accomplished through a 

 special organella is the pusules (Figs. 107, 108) in marine dinoflagel- 

 lates which, according to Kofoid and Swezy, appear to contain de- 

 composed organic matter and aid the organisms in carrying on this 

 process. The dissolved food matters are simpler compounds which 

 originate in animal or vegetable matter due to the decomposing 

 activities of bacterial organisms. Numerous free-living Zoomas- 

 tigina nourish themselves with this method. Recently a number of 

 investigators found that saprozoic Protozoa could be cultivated in 

 bacteria-free media of known compositions. For example, Prings- 

 heim observed in Polytoma uvella (Fig. 97, h) that sodium acetate 

 is needed from which the starch among others is produced and carbo- 

 hydrates have no direct bearing upon the nutrition, but fatty acids 

 derived from them participate in the metabolism. Hall, Jahn, 

 Loefer and others are following the same line of work which may lead 

 to a better understanding of saprozoic nutrition as found in Proto- 

 zoa. 



The Protozoa which live within the body of another organism are 

 able to nourish themselves by absorbing the digested or decomposed 

 substances of the host and could be considered as saprozoic, though 

 the term parasitic has sometimes been used. Coelozoic Protozoa be- 

 long to this group, as for example, Protociliata, astomatous ciliates, 

 Trypanosomatidae, etc. In the case of cytozoic or certain histozoic 

 forms, such as Cnidosporidia, the host cytoplasm is apparently 

 liquefied or hydrolyzed by enzymes before being absorbed by them. 

 The parasitic Protozoa, which actually feed on host tissue cells, such 

 as Entamoeba histolytica, Balantidium coli, etc., or endocommensals, 

 employ, of course, the holozoic nutrition. 



Many Protozoa nourish themselves by more than one method at 

 the same or different times, subject to a change in external condi- 



