6o THE AMOEBAE LIVING IN MAN 



Walker {vide Walker and Sellards, 1913) infected a man by feeding him 

 with cysts from the stools of another man — a convalescent carrier, who 

 had previously suffered from amoebic dysentery. The second man, 

 however, became a contact carrier. He acquired an infection with the 

 same strain of amoebae, but did not develop dysentery. From the cysts 

 in his stools a third man was then similarly infected. He also became 

 a contact carrier. But from the cysts in his faeces a fourth man was 

 infected, and he developed a typical attack of acute amoebic dysentery 

 twenty days after ingesting the cysts. It is difficult to conceive of any 

 more conclusive proof that it is the host, and not the parasite, which 

 determines whether an infection is "pathogenic" or "non-pathogenic." 



Baetjer and Sellards have recently attempted to show that there are 

 strains of E. histolytica with different degrees of virulence.* Although 

 this appears highly improbable, their experiments may be briefly noted 

 here, as their conclusions have been accepted by some workers. The 

 fullest account is given in the paper by Sellards and Baetjer (1915). i'"* 

 which three different " strains of E. histolytica " are described. The first 

 was obtained from a patient (Case A) with intestinal symptoms but no 

 dysentery. The amoebae in the stools were scanty, sluggish, and con- 

 tained no red blood corpuscles. Their nuclear characters were not 

 those typical of any of the intestinal amoebae of man.f "Cyst-like 

 bodies" with i, 2, or 3 nuclei were also found in the stools. A 

 specimen containing chiefly the "cyst-like bodies" was injected into 

 the caecum, ileum, and stomach of a kitten. Some weeks later the 

 animal passed a few " amoebae " and " cysts '" containing 4, 5, or 6 nuclei. 

 These are all figured, and are strikingly like cells from the kitten's 

 intestine, though unlike any developmental stages of E. histolytica. The 

 kitten was killed and its " amoebae " inoculated into two others. One 

 of these was also killed later, and " amoebae " were found in its large 

 intestine post nwrteiii. They were " not very well preserved, but 

 apparently approached the histolytica type." 



In the second case (Case B) amoebae "somewhat intermediate 

 between the coli and the histolytica types " were found. No figures are 

 given. A kitten inoculated with these "amoebae " developed dysentery, 

 but recovered " before any entirely satisfactory specimens were obtained 

 for morphological study." In the third case (Case C), no amoebae were 

 ever found in the patient — only " cyst-like bodies containing from one 

 to three nuclei." These were inoculated into the caecum and stomach 

 of a kitten, which developed a watery diarrhoea a month later, with 

 "amoebae" like those of Case A in its stools. Its symptoms abated, 

 and it was finally killed. Post uiortcm neither amoebae nor evidences of 

 amoebic infection were discoverable. 



It will be obvious from this brief summary that there is not much 

 evidence that Cases A, B, or C, or any of the experimentally " infected " 

 kittens, ever harboured amoeljae at all. Nothing greatly resembling 

 Entamoeba histolytica is described or figured from any human case 

 or kitten. 



* The authors consider that they were dealing with " atypical strains " of E. histo- 

 lytica modified by environment. 



t The authors only refer to E. coli and E. histolytica, and are apparently unaware 

 that any other species occur in man. 



