20 PBACTICAL PAEASITOLOGY 



membrane and large caryosome. Isolated developmental stages may 

 be observed, but it is impossible to follow the entire process, which 

 is very complicated, without long and tedious study. The life-history 

 of this organism is shown in fig. 2. It multiplies by simple fission 

 and by schizogony. The splitting up of the nucleus during schizogony 

 is very characteristic. The chromatin collects in eight portions upon 

 the surface of the nucleus, and from these simultaneously proceed, the 

 eight daughter-nuclei of the eight new organisms (fig. 2, 3 5). As 

 the faeces tend to become solid, in addition to dead Amoebae, young 

 cysts will be found. These originate in a casing of mucous matter 

 which forms round the ball-shaped Amoeba and which is followed at 

 a much later stage by the true hard cyst. Changes of the nucleus, 

 leading to self-propagation (autogamy), may be observed in the young 

 mucous cysts (figs. 2, 6 12), while in the older hard cysts the succes- 

 sive stages of nuclear multiplication, which result in the formation 

 of the eight daughter-cysts, may be seen (fig. 2, 12 13). Cats as 

 well as man may be infected with the mature encysted Amoebae, 

 which, when they reach the commencement of the large bowel in the 

 fresh host, burst and allow the young parasites to escape (fig. 2, 14). 



The intestinal Amoebae of animals should be studied and their 

 structure and development compared with those of the varieties found 

 in man. The E. muris (Grassi) is found in small numbers at the 

 commencement of the large bowel in about 50 per cent, of mice. 

 It is closely related to the E. coli and forms eight-nucleated cysts. 

 In the resting-state, however, the Amobae reproduce themselves, not 

 by multiple division of the nucleus and plasm, but by simple fission. 

 Like the intestinal Amoebae of man, they are not cultivable in artificial 

 media. The cysts of another variety of Amoeba, however, are found 

 in the faeces of mice, and these are readily cultivable by smearing 

 a small portion of the faeces upon the agar medium described above. 

 This organism is not parasitic ; its cysts pass unchanged out of the 

 bowel of the mouse, similarly to Chlamydophrys enchelys (Ehrbg.), 

 as described by Schaudinn. 1 



In the terminal portion of the intestinal canal of frogs, an 

 Infusorian, E. ranarum (Grassi), is found, generally in small numbers, 

 which resembles the E. coli. 



In the terminal portion of the intestinal canal of lizards (where, 

 later, we shall find Flagellates) two varieties of Amoeba, which have 

 no relationship to the parasitic Amoebae of man, are found. They are 

 readily cultivated upon the agar medium, and will repay the trouble 

 of observation. The one species, which is distinguished by its double 



1 Cf. C. M. Wenyon, "Observations on the Protozoa in the Intestine of Mice," 

 Arch. f. Protistenkunde, supp. i, 1907, pp. 169-201. 



