90 AMOEBAE LIVING IN MAN 



immagazzinato"). Schaudinn (1903) called them " chromidia," and 

 since then they have generally been so named. With the "chromi- 

 dium " of the shelled Rhizopods, however, they probably have nothing 

 in common. 



Mode of Infection. — What has been said already about the vitality 

 and powers of resistance of E. histolytica cysts is equally applicable to 

 E. colt, and need not be repeated. That the cysts are the forms which 

 convey infection from man to man there can be no doubt. Grassi 

 (1888) and Calandruccio (1890) state that they were able to infect 

 human beings by causing them to swallow the cysts of this species. 

 Schaudinn (1903) later asserted that he had twice* successfully performed 

 this experiment upon himself. Carefully conducted experiments made 

 later by Walker and Sellards (19 13) have proved conclusively that infec- 

 tion is brought about in this manner. They fed 20 men on cysts of 

 E. coli, belonging to 5 different strains (i.e., from the stools of 5 different 

 persons), and successfully infected 17 of them. Infection, as judged by 

 the appearance of cysts in the stools, was established in from i to 11 

 days after feeding — the average time being 4*7 days. 



The early stages in the development of the cyst in its new host are 

 still unknown. On analogy with other species, it is probable that the 

 cysts hatch in the small intestine, and liberate broods of 8 amoebae — or 

 possibly a single 8-nucleate amoeba, which later divides into 8 young 

 organisms — which pass into the large bowel, and there establish 

 themselves. 



Casagrandi and Barbagallo (1897) believed that they had been able 

 to observe these stages in cats. They claimed to have seen the cysts 

 hatch in the large intestine, and small amoebae emerge ; but they 

 believed that this development could only be observed in cats whose 

 intestines had been previously irritated and inflamed by a special method 

 of treatment. Their account is, to me, very unconvincing — as also is 

 their figure, which resembles an artificially ruptured cyst,f but is 

 supposed to show the emergence of the small amoebae. Schaudinn 

 {1903) stated that he had confirmed these observations, and that " the 

 results of my infection experiments on myself, and on experimental 

 animals, agree completely with the findings of the two Italian inves- 

 tigators." No other workers, apparently, have ever been able to infect 

 cats or any other animals with E. coli, or to observe any stages in their 

 •development in animals fed upon the cysts. Quincke and Roos, Darling, 

 Wenyon, Craig, and many other workers always obtained negative 



* This statement may well be questioned. Schaudinn stated that the infection 

 lasted on each occasion for only 2 months, and then disappeared spontaneously. It is 

 a remarkable observation, if true : for there can be no doubt that infections persist 

 usually for many months at least, and even for years, and I have never seen a single 

 case which has lost an infection with certainty whilst under observation. Apparent loss 

 is very common — the stools of infected persons often remaining "negative " for long 

 periods. Cf. Dobell (1917). Schaudinn's observations appear to me valueless, in the 

 absence of any adequate control experiments. It is not improbable that he was infected 

 with E. coh'heiore, during, and after his experiments, but merely failed to find the cysts 

 at certain examinations. 



t Werner (1912) has figured a similar burst cyst — stained — which is supposed to 

 illustrate the same stage ; but, as he naively remarks, the bursting in this case was " the 

 result of a trauma." It is by no means difficult to obtain such burst cysts — especially 

 with certain fixatives ; but it is difficult to see what connexion they can have with the 

 development of the amoeba. 



