PHYSIOLOGY 93 



only instance in which the saprozoic nutrition is accompHshed 

 through a special organella is the pusules (Figs. 101, 102) in ma- 

 rine dinoflagellates which, according to Kofoid and Swezy, ap- 

 pear to contain decomposed organic matter and aid the organ- 

 isms in carrying on this process. The dissolved food matters are 

 simpler compounds which have originated in animal or vegetable 

 matter due to the decomposing activities of bacterial organisms. 

 Numerous free-living Zoomastigina 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, Pringsheim observed in Polytoma 

 uvella (Fig. 91, h) that sodium acetate is needed from which the 

 starch among others is produced, and carbohydrates have no di- 

 rect bearing upon the nutrition, but fatty acids derived from 

 them participate in the metabolism. Hall, Jahn, Loefer and oth- 

 ers are following the same line of work which may lead to a better 

 understanding of saprozoic nutrition as found in Protozoa. 



The Protozoa which live within the body of another organism 

 are able to nourish themselves by absorbing the digested or de- 

 composed substances of the host and could be considered as sap- 

 rozoic though parasitic has sometimes been used. Coelozoic Pro- 

 tozoa belong to this group, as for example, Protociliata, astomous 

 ciliates, Trypanosomidae, etc. In the case of cytozoic or certain 

 histozoic forms, such as Cnidosporidia, the host cytoplasm is ap- 

 parently liquefied or hydrolyzed by enzymes (?) before being ab- 

 sorbed by the latter. The parasitic Protozoa, which actually feed 

 on host tissue cells, such as Entamoeba histolytica, Balantidium 

 coli, etc., or endocommensals, employ, of course, the holozoic nu- 

 trition. 



Many Protozoa nourish themselves by more than one method 

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

 conditions. This is sometimes referred to as mixo trophic nutrition 

 (Pfeiffer). For example, Euglena gracilis, according to Zumstein 

 (1889) and Lwoff (1932) loses its green coloration and becomes 

 Astasia-like in the dark, or even in the light when the culture me- 

 dium is very abundant in decomposed organic substances, which 

 would indicate that this organism is capable of carrying on both 

 holophytic and saprozoic nutrition. On the other hand Chloro- 

 gonium euchlorum and C. elongatum are said, according to Loefer 

 (1934), to retain their green coloration after a year of cultivation 



