72 THE AMOEBAE LIVING IN MAN 



other protozoa. Moreover, it is clear that the amoebae which he 

 observed were intestinal amoebae, and not free-living species. These 

 are probably the first recorded observations on the intestinal amoebae of 

 man ; and as Cunningham's early work has hitherto received but scant 

 attention,* and is not easily accessible, I shall consider it in some detail. 



Cunningham was fully alive to the possible errors involved in examin- 

 ing stools for amoebae. " There is," he writes, " a considerable amount 

 of difficulty and numerous sources of fallacy to be encountered in pro- 

 ceeding to the consideration of amoebae" (1871, p. 44) — a remark which 

 his successors might have taken to heart with much profit to science and 

 themselves. He notes further that he distinguished his amoebae from 

 cells in the stools by their " power of free progression," and he observes 

 that they rapidly die outside the human body. He speaks of both free 

 and "encysted" amoebae, but most of the latter — though probably not 

 all — were merely rounded and motionless individuals. For the first 

 time he observed and recorded that the intestinal amoebae differ from 

 free-living species in possessing no " contractile vesicles." It is clear 

 from his later work — though not from the earlier — that Cunningham 

 (1881) saw both the free forms and the cysts of Euiamoeba coli. " They 

 occur in the excreta during health, as well as in cases of cholera and 

 other morbid conditions affecting the intestinal canal " (Cunningham 

 (1881), p. 248). His text-fig. 4 depicts the cysts, and text-figs. 5 and 6 

 show the free amoebae — the last being an unmistakable E. coli con- 

 tiining ingested Blasfocysfis ("sporoid bodies"). "In the encysted 

 condition, when their form is more or less spherical or elliptical, they 

 frequently attain a diameter of 25 /x or even more, and they may range 

 downward from this until their diameter only amounts to 8 /x " (p. 249). 

 From the last remark it seems probable that he observed the cysts of 

 more than one species. He notes the variable size and shape of the 

 amoebae, the " changeable vacuoles, often of considerable size," and 

 again the absence of a contractile vacuole. Of the nucleus he says that 

 it was not always visible, that it " may or may not include a visible 

 nucleolus," that it may attain a diameter of 7-9 fi; and that "it is 

 circular and apparently discoid, but in some cases may appear annular 

 from the presence of a thickened margin " (p. 249). I believe nobody 

 who reads Cunningham's account and studies his pictures can fail, if he 

 knows this organism, to recognize in them the commonest of the 

 intestinal amoebae of man — Entamoeba coli. 



Unfortunately, in his later work Cunningham was led astray by the 

 flagellates and other organisms which developed in his material : and he 

 combined together all the organisms which he found in faeces — includ- 

 ing the intestinal amoebae and flagellates, which he had accurately 

 observed — to form the life-history of a single organism which he named 

 " Protomyxomyces coprinariiis," and regarded as a sort of Mycetozoon. 



After Cunningham, Grassi (!879<i!) described amoebae from human 

 faeces, and identified them with the organisms then recently discovered 

 by Losch (1875). Accordingly, he named tiiem "Amoeba coli Losch." 

 Now there can be little doubt that Grassi was mistaken in this. The 



* Craig (1908) has stated that Grassi (1888) "was probably the first investigator to 

 demonstrate the occurrence' of amoebae in the faeces of healthy individuals" (p. 332) ; 

 and he adds that Cunningham "was probably observing developmental stages of 

 flagellates." Few readers of Cunningham's works are likely to share these views. 



