ENTAMOEBA HISTOLYTICA 69 



have unsuccessfully attempted to infect the rabbit. But Huber (1909) 

 claims to have succeeded, and his observations, though little noticed, are 

 of considerable interest. He says he succeeded in infecting 4 out of 8 

 rabbits fed on human stools containing cysts of E. histolytica. They 

 did not acquire dysentery or diarrhoea, nor did they pass amoebae with 

 their faeces. Three died after 3 — 5 weeks, and the fourth was killed. 

 Post mortem examination showed that the amoebae were localized in 

 ulcers in the caecum. The ulceration was characterized by great inflam- 

 matory thickening of the submucosa, and was different from that usually 

 seen in man and the cat. It would be interesting to know whether the 

 rabbit can become a carrier of E. histolytica — like a human being ; and 

 Ruber's results seem to indicate the importance of fuller inquiry. 



Unsuccessful attempts have been recorded to infect rats (Werner 

 (1908), Dale and Dobell (1917), Chatton (19186), etc.) ; mice (Chatton, 

 19176, 19186) ; and a gerbil (Kruse and Pasquale, 1894). Lynch (19156), 

 however, claims to have succeeded in the case of the rat, and also to 

 have observed spontaneous amoebic dysentery in this animal. Although 

 he gives a circumstantial account of the lesions, and appears to be in no 

 doubt about the identity of his amoebae with E. histolytica, his descrip- 

 tion of the parasites is very unconvincing. He seems, moreover, to 

 be unaware that rats are sometimes infected with another species of 

 amoeba (£. mitris ?), which may possibly account for his findings — as 

 Chatton (1917^) has pomted out. Lynch's conclusions can hardly be 

 accepted without further evidence. Kartulis {1891), it may be added, 

 had previously stated that rats may suffer from spontaneous amoebic 

 dysentery. 



Experiments on monkeys, and the amoebae naturally occurring in 

 these animals, will be considered in another place. {Vide p. 131 infra.) 



Dissemination. — It is clear that E. histolytica infection is normally 

 conveyed from man to man by the contamination of food or drink 

 with faecal matter containing the cysts of the parasite. The spread of 

 infection must always depend, therefore, upon defective sanitary condi- 

 tions — as is verified by the evidence which has accumulated showing 

 that infections with this organism are commonest in the tropics and 

 other places where hygienic conditions are worst. Infection is probably 

 acquired in many cases by drinking water polluted with faeces containing 

 cysts of £. histolytica. It has also been shown by Wenyon and 

 O'Connor (1916, 1917), that flies may act as spreaders of infection : for 

 flies will feed readily upon human faeces containing cysts, and can pass 

 these intact through their bodies and out in their own faeces. It thus 

 seems probable that the fly is often an important agent in spreading 

 E. histolytica in nature. It should be noted, however, that some other 

 workers have regarded the activities of the fly in this connexion from a 

 different standpoint. Roubaud (1918) suggests, indeed, that the fly is 

 beneficial rather than harmful : for its faeces rapidly undergo desiccation 

 when deposited ; and any cysts which it may pass are thus, in ordinary 

 circumstances, rapidly destroyed. 



Cultivation. — Many workers have, in the past, attempted to cultivate 

 E. histolytica. The earlier of them often claimed to have succeeded, but 

 it is now generally recognized that they merely cultivated free-living 

 amoebae from the stools. The original claim of Kartulis (1891) was 

 disposed of by Celli and Fiocca (1894, 1894(7, 1895) and Casagrandi and 

 Barbagallo (1895a, 1897, i897fl), who arrived at the true explanation of 



