THE SARCODINA 



225 



fission of the ordinary type, and also by a process of multiple fission is 

 which the nucleus divides until there are eight nuclei in the body ; the 

 characteristic 8-nucleate plasmodium then divides up into eight small 

 amoebae, each of which grows into an ordinary adult form. Hence it in 

 characteristic of E. coli to occur in various sizes, from very small to full-grown 

 amoebae. 



The propagative phase of E. coli is initiated by the formation of a gelatinous 

 envelope round a full-sized amceba possessing a single nucleus. The nucleus 

 then divides into two, and the process of maturation and autogamy takes place 

 that has been described on p. 139, supra (Fig. 73). When it is complete, a 

 tough resistant cyst is formed within the soft gelatinous envelope, and each 

 of the two synkarya divides twice to produce four nuclei. Thus is formed 

 the 8-nucleate resistant cyst which is characteristic, perhaps diagnostic, 

 of this species. Within the cyst no further changes take place until it is 

 swallowed by a new host ; then it 

 is believed that the contents of the 

 cyst divide up into eight uninucleate 

 amcebulae, which are set free in the 

 colon and are the starting- point of 

 a new infection. Schaudinn was 

 able to infect himself by swallowing 

 the 8-nucleate cysts of the amceba. 



Prowazek (A.P.K., xxii., p. 345) 

 has described a variety of E. coli 

 under the name E. williamsi. 



E. Jiistolytica reproduces itself in 

 the amoeboid phase by binary fission 

 and by a process of gemmation in 

 which the nucleus multiplies by 

 division, and then small amcebulae, 

 each with a single nucleus, are 

 budded off from the surface of the 

 body. In the process of gemma- 

 tion, however, the number of nuclei 

 in the body is irregular, and not 

 definitely eight, as in E. coli. In 

 its propagative phase E. Jiistolytica 

 does not form a cyst round the 

 whole body, but its nucleus becomes 

 resolved into chromidia, which 

 collect in patches near the surface 

 of the body. Little buds are then 

 formed as outgrowths of the body, 

 each bud containing a clump of 

 chromidia. Round each bud a 

 sporocyst is formed of so tough and 

 impervious a character that no 

 further cy^ological study of the 

 bud is possible. The resistant spores formed in this way separate from the 

 body, of which the greater part remains as residual protoplasm and dies off. 

 The minute spores are the means of infecting a new host, as shown by 

 Schaudinn in experiments on cats, which are particularly susceptible to the 

 attacks of this amceba. 



Schaudinn's investigations, of which a brief summary has been given in 

 the foregoing paragraphs, first introduced clear ideas into the problem of the 

 human entozoic amoebae. Many of the works of subsequent investigators 

 have tended, however, rather to confuse and perplex the question, for various 

 reasons. In the first place, in cultures made from human faeces, free-living, 

 non- parasitic species of amoebae make their appearance, which have passed 

 through the digestive tract in an encysted condition, and emerge from their 



15 



FIG. 90. Entamceba Jiistolytica. A, Young 

 specimen; B, an older specimen crammed 

 with ingested blood-corpuscles ; C, D, E, 

 three figures of a living amceba which 

 contains a nucleus and three blood- 

 corpuscles, to show the changes of form 

 and the ectoplasmic pseudopodia : n., 

 nucleus ; b.c., blood-corpuscles. After 

 Jiirgens. 



