28 PROTOZOOLOGY 



not yet been comprehended. Certain strains of bacteria were found 

 by Hardin (1944) to be toxic for Paramecium multimicronucleatum, 

 but if Oikomonas termo was present in the culture, the ciliate was 

 maintained indefinitely. This worker suggested that the flagellate 

 may be able to "detoxify" the metabolic products produced by the 

 bacteria. Food relation in ciliates (Faure-Fremiet, 1950, 1951a). 



The adaptability of Protozoa to varied environmental conditions 

 influences their distribution. The degree of adaptability varies a 

 great deal, not only among different species, but also among the 

 individuals of the same species. Stentor coeruleus which grows ordi- 

 narily under nearly anaerobic conditions, is obviously not influenced 

 by alkalinity, pH, temperature or free carbon dioxide in the water 

 (Sprugel, 1951). 



Some protozoans inhabit soil of various types and localities. Un- 

 der ordinary circumstances, they occur near the surface, their maxi- 

 mum abundance being found at a depth of about 10-12 cm. (Sandon, 

 1927). It is said that a very few protozoans occur in the subsoil. 

 Here also one notices a very wide geographical distribution of ap- 

 parently one and the same species. For example, Sandon found 

 Amoeba proteus in samples of soil collected from Greenland, Tristan 

 da Cunha, Gough Island, England, Mauritius, Africa, India, and 

 Argentina. This amoeba is known to occur in various parts of North 

 America, Europe, Japan, and Australia. The majority of Testacea 

 inhabit moist soil in abundance. Sandon observed Trinema enchelys 

 in the soils of Spitzbergen, Greenland, England, Japan, Australia, St. 

 Helena, Barbados, Mauritius, Africa, and Argentina. 



Parasitic Protozoa 



Some Protozoa belonging to all groups live on or in other organ- 

 isms. The Sporozoa are made up exclusively of parasites. The rela- 

 tionships between the host and the protozoan differ in various ways, 

 which make the basis for distinguishing the associations into three 

 types as follows: commensalism, symbiosis, and parasitism. 



Commensalism is an association in which an organism, the com- 

 mensal, is benefited, while the host is neither injured nor benefited. 

 Depending upon the location of the commensal in the host body, 

 the term ectocommensalism or endocommensalism is used. Ecto- 

 commensalism is often represented by Protozoa which may attach 

 themselves to any aquatic animals that inhabit the same bod}' of 

 water, as shown by various species of Chonotricha, Peritricha, and 

 Suctoria. In other cases, there is a definite relationship between the 

 commensal and the host. For example, Kerona polyporum is found 



