PATHOGENIC IMPORTANCE 



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posed have been furnished recently by the findings in returned 

 British soldiers, in whom uncomplicated infections with flagel- 

 lates have been found in many dysenteric cases, and also by the 

 investigations of Lynch, Barlow, Escomel and others in various 

 parts of the world. Still further evidence is furnished by the 

 fact that parasites very closely allied to species found in man 

 have recently been shown to be unquestionably of pathogenic 

 importance, at least under certain conditions, in lower animals. 



Obviously, however, in view of the large number of infected 

 persons, the intestinal protozoans must often have little or no 

 pathogenic effect. There is, nevertheless, much individual dif- 

 ference in susceptibility, and different strains of the same para- 

 site seem to vary in the effects they produce. Moreover it is 

 highly probable that a great many slight and perhaps almost 

 unnoticed symptoms, resulting in a certain amount of interference 

 with the digestive tract and in a general lowering of the health, 

 may find their ultimate cause in intestinal parasites, either pro- 

 tozoans or worms or both. The health of people living in warm 

 and tropical countries, even aside from the effects of malaria and 

 other warm-climate diseases, is proverbially less perfect than that 

 of people in the usually more sanitary northern countries. It is 

 quite probable that intestinal Protozoa may play a part in this 

 lowering of the tone of health. 



In the paragraphs below a brief account of the more important 

 intestinal flagellates and ciliates is given, with what is known of 

 their pathogenic effects, in the following order: (1) the bi-flagel- 

 late forms, Bodo, Cercomonas and Embadomonas, (2) the multi- 

 flagellate forms, Trichomonas, Enteromonas, Chilomastix and 

 Giardia; and (3) the ciliate, Balantidium. 



Bi-flagellate Protozoa 



Most primitive of the intestinal flagellates are the bi-flagel- 

 lated forms, several genera of which have been found in the human 

 intestine. The relation of these animals to the still more primi- 

 tive mono-flagellated trypanosomes and their allies is shown 

 by the parasites of the genus Trypanoplasma. The animals of 

 this genus resemble trypanosomes in the general form of the body 

 and in the possession of a parabasal body and an undulating 

 membrane, but have an additional free flagellum. In Cercomonas 



