64 THE AMOEBAE LIVING IN MAN 



bacterial parasite. In both these cases, and at least one other which I 

 have seen, the parasitic bacteria appeared to be identical. They were 

 cocco-bacilli of the form shown in figs. 83-85, PI. V. 



I would also note here that the chromatoid bodies of E. histolytica 

 may be mistaken for bacteria when, as sometimes happens, they are in 

 the form of slender rods, filaments, or small granules. As noted else- 

 where, these bodies may occur not only in the cysts but also in the pre- 

 cystic amoebae (fig. 82, PI. V) ; and such amoebae may easily be misin- 

 terpreted as precystic individuals containing ingested bacteria. 



When precystic or other amoeboid forms of E. histolytica contain 

 ^* ingested bacteria " it is therefore necessary to prove (i) that these are 

 not really chromatoid bodies, or, if really bacteria, (2) that they are 

 not parasites or (3) organisms which have invaded the dead or dying 

 amoebae. I cannot find, however, that Kuenen and Swellengrebel, or 

 any other workers who share their view, have attempted to exclude any 

 of these sources of fallacy. Until they do, their statement that E. his- 

 tolytica can feed upon bacteria is not supported by any evidence. The 

 mere finding of " bacteria " in amoebae by no means proves that E. his- 

 tolytica is capable of living as a commensal. 



Kuenen and Swellengrebel (1913) also describe a case in which they 

 found "mimtta" forms of E. histolytica containing starch grains, in 

 addition to bacteria. At first sight this appears puzzling. But the 

 explanation is at once found when, a little later, we read that this case 

 also passed 8-nucleate cysts of E. histolytica. I have not the slightest 

 doubt that this case was really infected with E. coli, and that the small 

 amoebae containing starch grains and bacteria, and the 8-nucleate cysts, 

 all really belonged to this species. To the three postulates made in the 

 previous paragraph it thus seems necessary to add a fourth — that when, 

 in a stool, "amoebae" are found containing bacteria, some proof that 

 they belong to E. histolytica shall be required. 



From the foregoing considerations it therefore appears to me highly 

 improbable that E. histolytica can alter its mode of life so fundamentally 

 as to become a mere commensal like E. coli : and in support of such 

 a view — which is entirely opposed to my own experience, and to me 

 almost inconceivable — I can find no evidence whatsoever. 



Sexual Phenomena. Conjugation. — No conjugation of any sort has 

 been shown to occur at any stage in the life-history of E. histolytica. It 

 is sometimes stated that Schaudinn (1903) described an autogamy in the 

 cysts of this species : and although this is incorrect, such a process 

 was actually described by Hartmann (1908) in " E. teiragena" — really 

 the same species. As I pointed out at the time (Dobell, 1909), his inter- 

 pretation was not justified, and the alleged "autogamy" was disproved 

 later by Walker* (1911). 



Sexual stages in the life-history have been suggested by several 

 workers, but are still unsupported by evidence. Job and Hirtzmann 



• Walker gives me the credit of having pointed out that the development in the 

 cysts is by " straightforward nuclear division": but he is not quite correct in stating 

 that I came to this conclusion in the case of E. coli. 1 proved it in E. ranarutn, and 

 pointed out that the development of E. histolytica (then called " E. tetragena ") was 

 probably "almost identical." At that time I was still in doubt about the development 

 of E. coli, owing to the very definite statements of Schaudinn (1903), and Wenyon's 

 (1907) " confirmation " in E. muris. 



