SURVEY OF INVERTEBRATES 53 



2. PARASITIC PROTOZOA 



1. PHOTOZOA OF THE ALIMENTARY TRACT OF VERTEBRATES AND OF 

 RELATED HABITATS 



A. Culture experiments. Culture experiments have 

 demonstrated that protozoa which live in the alimentary 

 tract or in physiologically related habitats in vertebrates 

 (uterus, vagina) have well-developed anaerobic func- 

 tions. The following forms have been cultured under 

 more or less strictly anaerobic conditions : intestinal Tri- 

 chomonads (Andrews, 1926; Cleveland, 1928 and 1928a), 

 TricJiomonas foetus (Witte, 1933), Trichomonas vagin- 

 alis (Johnson, 1941), Endamoeha histolytica (Dobell and 

 Laidlaw, 1926; Snyder and Meleney, 1941, 1942, 1943), 

 Balantidium (Barret and Yarbrough, 1921; Scott, 1927; 

 Pritze, 1928 ; Schumaker, 1931 ; Tanabe and Komada, 

 1932; Nagahana, 1932; Levitanskaja, 1938), ciliates par- 

 asitizing the stomach of ruminants (Knoth, 1928; West- 

 phal, 1934; Hungate, 1941, 1942, 1943), Nyctotherus and 

 opalinids from the frog (Piitter, 1905; Konsuloff, 1922). 



It is a well-established fact that these species, with the 

 exception of the rumen ciliates and perhaps the opalinids, 

 can also be cultured when the surface of the medium is 

 freely exposed to the atmospheric air. Balantidium coli 

 can, as Schumaker (1931) has shown, even withstand an 

 oxygen pressure of 18 lbs. per square inch for 32 hours. 

 It is difficult in many cases to know with certainty, how- 

 ever, whether appreciable amounts of oxygen are present 

 in those layers of the media in which the parasites pre- 

 dominantly occur, i.e., wdiether ditfusion from the sur- 

 face is sufficient to bring about an equilibrium with the 

 atmosphere. With the exception of some Trichomonas, 

 the protozoa were grown in mixed cultures with bacteria. 

 This, of course, complicates the situation considerably. 

 The bacteria usually have a high rate of oxygen consump- 

 tion, and since the depth of the media commonly em- 

 ployed in the culture of parasitic protozoa is rather con- 

 siderable, it seems likely that the oxygen tension will be 



