240 



THE QUARTERLY REVIEW OF BIOLOGY 



All of the protozoa usually recognized 

 by protozoologists as human parasites are 

 listed in the above table. Many species 

 described from monkeys have not been 

 included, however, because of their more 

 or less doubtful validity; this applies par- 

 ticularly to amoebae, trypanosomes, and 

 malarial organisms. Further study may 

 prove that certain of these are specifically 

 distinct, but at present our information 

 regarding them is for the most part too 

 scanty to warrant definite decisions. 



The table shows that of the four genera 

 of amoebae that live in man, three are 

 represented among monkey amoebae and 

 the fourth has probably not yet been 

 discovered on account of its rarity. Four 

 of the six well-authenticated species of 

 human amoebae are indistinguishable 

 from four species of amoebae that have 

 been described from monkeys. No 

 amoebae in monkeys have been found 

 corresponding to two of the human 

 species, Endamoeba gingivalis of the mouth 

 and Dientamoeba fragilis of the intestine. 

 Among the intestinal flagellates of mon- 

 keys are five species that are indistinguish- 

 able from five of the seven species that 

 live in man; Trichomonas buccalis of the 

 mouth and Tricercomonas intestinalis of the 

 intestine of man appear to be absent in 

 monkeys. The ciliate, Balantidium coli, 

 that lives in man is probably the same 

 species that has been recorded from 

 various species of monkeys. Certain 

 monkeys are infected with a genus of 

 ciliates, Troglodytella, of which two species 

 and one variety have been described, that 

 has no representatives in man. All three 

 species of human trypanosomes seem to 

 be present as natural parasites of monkeys. 

 The leishmanias have not been reported 

 from monkeys. Malarial parasites that 

 occur in monkeys resemble the three 

 species that live in man. The coccidium, 

 Isospora hominis, of the human intestine 



and the sarcosporidia that have been 

 reported a few times as muscle parasites 

 of man have not been recorded from 

 monkeys. No parasite corresponding to 

 Babesia pithed of monkeys occurs in man. 

 Thus eleven of the fifteen genera of human 

 protozoa are known to have representa- 

 tives in monkeys; and seventeen of the 

 twenty-five species of human protozoa 

 have been described from monkeys. One 

 genus of ciliates, Troglodytella, and one 

 Babesia occur in monkeys but not in man. 



GENERA AND SPECIES OF PROTOZOA IN 

 LOWER ANIMALS 



The significance of this situation can 

 best be realized by comparing the proto- 

 zoan parasites of man with those of other 

 lower animals. Such a comparison brings 

 out the fact that although many lower 

 animals are inhabited by protozoa belong- 

 ing to certain of the same genera as those 

 of man the species can be distinguished 

 without difficulty from human protozoa. 

 Thus the rat is infected with species of 

 intestinal amoebae (e.g., Endamoeba muris) 

 and intestinal flagellates (e.g., Giardia 

 muris, Trichomonas muris), and with blood- 

 inhabiting flagellates (Trypanosoma lewisi), 

 but not a single species of the rat is 

 considered by protozoologists to be iden- 

 tical with any human species. Certain 

 genera and many species, however, have 

 been described from rats that do not occur 

 in man. Other mammals whose proto- 

 zoan parasites are fairly well known, such 

 as cats, dogs, guinea-pigs, pigs, sheep, 

 cattle and horses, are similar to rats in 

 this respect. Spontaneous infections in 

 lower animals with human protozoa have 

 been observed, for example, cats and dogs 

 with amoebiasis apparently due to Enda- 

 moeba histolytica, and rats with giardiasis 

 as a result of ingesting cysts of the human 

 giardia, G. lamblia, and in many of them 

 infections with human protozoa can be 



