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THE QUARTERLY REVIEW OF BIOLOGY 



toms do not appear. In these respects 

 this type of monkey amoeba resembles 

 E. histolytica of man; the latter is present 

 in about ten per cent of healthy human 

 beings in the general population but 

 occasionally gives rise to dysentery and 

 liver abscesses. No morphological differ- 

 ences have yet been found for distinguish- 

 ing between E. nuttalli of monkeys and 

 E. histolytica of man. 



Are monkeys susceptible to infection 

 with E. histolytica from man, and can man 

 be infected with E. nuttalli from monkeys? 

 Evidence on cross-infection is available 

 from both epidemiological observations 

 and from laboratory experiments. In the 

 first place most of the monkeys in which 

 amoebae have been found had been in 

 captivity, and hence associated with 

 human beings for various lengths of time. 

 They may thus have become infected with 

 cysts from man. As noted above, the 

 infected chimpanzee reported by Suldey 

 was a captive animal. Mathis (1913) 

 described an infection with a histolytica- 

 like amoeba (Endamoeba duboscqi, figs. 

 1 a, ib) in a macaque (Macaws rhesus) 

 that had been in Germany for 16 years; 

 in this case an original infection must 

 have lasted for that length of time or 

 else the monkey became infected with 

 human amoebae while in captivity, or 

 possibly with amoebae from other mon- 

 keys with which it was associated. 

 On the other hand, McCarrison (1919), 

 as a result of studies on 36 young monkeys 

 (Macacus sinicus) in India, states that 

 "monkeys in a wild state in S. India may 

 be carriers of E. tetragena (histolytica)." 

 Successful attempts to infect monkeys by 

 inoculating them with trophozoites or 

 cysts of E. histolytica from man have been 

 reported by several investigators. Thus 

 Franchini (1912.) claims to have infected 

 a monkey (species not given) with E. 

 histolytica per rectum. Kessel (19x6a) 



fed cysts of E. histolytica to two amoeba- 

 free monkeys (Macacus) and recovered 

 trophozoites and cysts from their feces 

 racially indistinguishable from the type 

 of amoebae fed to them, and, after autopsy, 

 found similar specimens in histological 

 sections. 



There is also epidemiological evidence 

 that the histolytica-like amoebae from 

 monkeys are infective to man; for example, 

 infections with this type of amoeba in 

 three individuals in Baltimore have been 

 traced to a colony of rhesus monkeys 

 maintained for experimental purposes. 



The laboratory animals most susceptible 

 to infection with E. histolytica from man 

 seem to be young cats of about 500 grams 

 in weight. Infections in kittens have 

 been established by feeding them cysts, 

 and by injecting trophozoites or cysts 

 (Hoare, 192.5) into the colon per rectum. 

 Mello (19x3) reports the infection of 

 kittens by the rectal injection of dysenteric 

 feces of monkeys (Macacus sinicus). 

 Dobell (1916) likewise succeeded in infect- 

 ing kittens with histolytica-like amoebae 

 from monkeys (Macacus rhesus and M. 

 sinicus) but states that the resulting 

 dysentery differs from that produced by 

 E. histolytica from man. The infection of 

 two cats, 6 and 7 months old respectively, 

 by rectal injections of feces containing 

 cysts of naturally infected monkeys was 

 obtained by Kessel (1916a). Two months 

 after injection the cats at autopsy were 

 found to contain trophozoites in the 

 upper colon and cecum and also in the 

 tissues of the intestinal wall. In a later 

 paper Kessel (1917) reports the successful 

 infection of 8 of 13 kittens with tropho- 

 zoites or cysts of histolytica-like amoebae 

 from monkeys; 6 of the kittens succumbed 

 to dysentery of the type induced in these 

 animals by E. histolytica from man. 



The methods introduced by Boeck and 

 Drbohlav (192.5) for cultivating human 



