140 



Still anotner possible factor in the distribution of dysentery 

 amebse is the rat. Dr. Lynch of Charleston, S. C., states that in 

 that city rats suffer from amebic dysentery as well as man. 

 The fact that rats became infected by eating infected human 

 fseces, the frequent occurrence of the disease in rats in houses 

 where human amebic dysentery has occurred, and the ready 

 transmission of the disease from rat to rat indicate that the rat 

 infection is identical with that in man, and is not due to the ameba 

 peculiar to rats, E. muris, and that rats may play an important 

 role in the spread of the human infection. It may be that rat 

 destruction will prove to be an important preventive measure 

 against amebic dysentery. Chatton has recently transmitted the 

 disease to guinea pigs also. 



Other Intestinal Amebae. As stated above there are a number 

 of other species of amebse which occur as human parasites, but as 

 compared with E. histolytica most of them are of little importance. 

 They are not tissue parasites, except possibly Councilmania 

 lafleuri, but feed principally if not exclusively on bacteria or dead 

 organic matter with which they are associated in the intestine. 

 Their principal importance lies in the possibility of their confusion 

 with the dysentery amebse. 



One of the commonest species is Endamceba coli. In stained 

 preparations this species can be distinguished from E. histolytica, 

 which it resembles in size and habitat, by the characteristics 

 given on p. 133, (cf. also Figs. 36 and 37). E. coli is usually 

 more sluggish in movement than E. histolytica. It never con- 

 tains blood corpuscles, but the body is often filled with nu- 

 merous food vacuoles containing bacteria or' other material 

 ingested from the intestinal contents (Fig. 37A). The cysts 

 of E. coli (Fig. 37B) are, on the average, larger than those of 

 E. histolytica, but as with the latter species there are races dis- 

 tinguishable by the size of the cysts. The average sizes in differ- 

 ent races vary from 15 /z to about 22 jj,. The mature cysts nor- 

 mally contain eight nuclei in contrast to the four usually found in 

 E. histolytica. Even in the four-celled stage the cyst can readily 

 be distinguished from those of E. histolytica by the eccentric 

 position of the karyosomes of the nuclei. According to Dobell 

 " E. coli has been found living as a harmless commensal in the 

 colon of man wherever and whenever it has been sought : no race, 



