ENTAMOEBA HISTOLYTICA 67 



justification, and are therefore confusing, I am unable to criticize their 

 conceptions. I find nothing to support their view, and do not understand 

 why they do not adopt the simple, obvious, straightforward, and consistent 

 interpretation of Walker and most other workers. 



Animal Infections. — Entamoeba histolytica is the only amoeba which 

 has been proved to be able to live in more than one host. Man is its 

 normal host, in all probability, but other animals can be experimentally 

 infected. Losch (1875), as already noted, infected a dog ; and Hlava 

 (1887), Kruse'and Pasquale (1894), Harris (1901), and Dale and Dobell 

 (1917) also succeeded in infecting this animal. The animal most readily 

 infected is, however, the cat, to which the amoeba has been successfully 

 transmitted by a large number of workers.* The earlier workers infected 

 cats by injecting amoebae from human dysenteric stools into the large 

 intestine per aiium, and this method is frequently successful. They 

 found, as was to be expected, that no infection took place if the amoebae 

 were administered per os — a fact often since confirmed. Quincke and 

 Roos (1893) found, however, that cats can be infected by causing them 

 to swallow the cysts of E. histolytica, and this too has been frequently 

 confirmed by later workers.f There is no good evidence that the cat 

 can be infected in other ways.ij: 



The cat, when infected, typically aquires acute and fata! amoebic 

 dysentery, closely resembling the comparable condition seen in man. 

 Spontaneous recovery takes place very exceptionally, and the cat, in all 

 probability, never becoines a carrier. The parasite appears to be in- 

 capable of forming cysts in the cat's intestine (cf. Dale and Dobell, 1917). 

 The "cysts" described in cats by several authors were almost certainly 

 not cysts of E. histolytica, for no competent workers who have studied 

 the infections in cats have ever seen cyst-formation in this animal. 

 There is already a large amount of evidence on this head. For example, 

 Dale and I (1917) studied about 150 kittens infected with £. histolytica, 

 but in spite of the most careful search never discovered any cysts 

 in them. This is in complete agreement with the observations of 

 Wenyon (1912) and many other careful workers. 



Darling (1913 c) found " uninucleate cysts" in an infected kitten, but 

 it is highly probable that they were merely rounded amoebae. The 

 "cysts " of E. histolytica observed in cats by Sellards and Baetjer (1915) 

 were obviously cells. Their description and figures make this clear — 

 their " cysts " being quite unlike those of E. histolytica, and containing 

 sometimes 5 or 6 nuclei. In an earlier paper (Baetjer and Sellards, 1914) 

 they stated that " encystment frequently occurred " in their infected 

 cats, but advanced no evidence. They have also stated (Baetjer and 

 Sellards, 1914a) that they produced " a carrier state" in cats; but they 



• See, for example, Hlava (1887), Kartulis (1891), Kovacs (1892), Quincke and Roos 

 (1893), Kruse and Pasquale (1894), Jiirgens (1902), Wenyon (1912), Darling (1913a), 

 Baetjer and Sellards (1914), Dale and Dobell (1917), etc. 



t Cf. Huber (1903, 1909), Kuenen and Swellengrebel (1913), Wenyon and O'Connor 

 (1917), Dale and Dobell (1917), etc. 



t The fantastic experiments of Lesage (1907 a) are hardly worthy of mention. He 

 claimed to have infected cats by placing stale dysenteric stools or liver abscess pus up 

 their noses, by injecting similar material hypodermically, by putting the dried blood of 

 an infected cat into the nose of another, and by other extravagantly impossible 

 methods. 



