PHYSIOLOGY 109 



able to nourish themselves by absorbing the digested or decomposed 

 substances of the host and could be considered assaprozoic, though 

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

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

 Trypan osomatidae, 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 endo commensals, 

 {Endamoeba blattae, Entamoeba coli, etc.) employ, of course, the holo- 

 zoic nutrition. 



Many Protozoa nourish themselves by more than one method at 

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

 tions. This is sometimes referred to as mixotrophic nutrition (Pfeif- 

 fer). For example, Euglena gracilis, according to Zumstein (1900), 

 Lwoff (1932) and Pringsheim and Hovasse (1948), loses its green 

 coloration in the darkness or even in the light when the culture 

 medium is very abundant in decomposed organic substances, which 

 may indicate that this organism is capable of carrying on both holo- 

 phytic and saprozoic nutrition. 



With the introduction of bacteria-free culture technique in recent 

 years, it has now become well established that a protozoan species 

 exhibits conspicuous differences in form, size and structure, which 

 are exclusively due to differences in the kind and amount of food 

 material. For example, Kidder, Lilly and Claff (1940) noted in 

 Tetrahymena vorax (Fig. 39), bacteria-feeders are tailed (50-75^ 

 long), saprozoic forms are fusiform to ovoid (30-70/x long), forms 

 feeding on sterile dead ciliates are fusiform (60-80^ long), and carni- 

 vores and cannibals are irregularly ovoid (100-250^ long), in the latter 

 form of which a large "preparatory vacuole" becomes developed. 

 In Chilomonas Paramecium, Mast (1939) observed the individuals 

 grown in sterile glucose-peptone solution were much smaller than 

 those cultured in acetate-ammonium solution and moreover the 

 former contained many small starch grains, but no fat, while the 

 latter showed many larger starch grains and a little fat. Amoeba 

 proteus when fed exclusively on Colpidium, became very large and 

 extremely "fat" and sluggish, growing and multiplying slowly, but 

 indefinitely; when fed on Chilomonas only, they grew and multi- 

 plied for several days, then decreased in number and soon died, but 

 lived longer on Chilomonas cultured in the glucose-peptone. It is 

 well known that Protozoa as any other organism, show atypical 

 or abnormal morphological and physiological peculiarities. In the 



