226 THE PROTOZOA 



cysts in the cultures ;* such amoebae, for the most part of the Umax-type, 

 have been confused with the true entozoic amoeba, and have given rise to 

 erroneous ideas. Secondly, it is certain now that the two species of amoebae 

 recognized by Schaudinn does not exhaust the list of human entozoic amoebae. 

 Thirdly, it is possible that Schaudinn did not see the entire life-cycle of the 

 forms studied by him, or that in some cases he confused stages of different 

 species in the same life-cycle (compare Hartmann, 247). 



It is still doubtful how many species of entozoic amoebae occur in man. 

 Hartmann recognizes two dysenteric amoebae, in addition to the harmless 

 E. coli : E. histolytica, Schaudinn, and E. tetragena, Viereck (synonym, E. 

 africana, Hartmann). E. tetragena has been described from various parts 

 of the tropics ; it differs from E. histolytica in its characters, and more nearly 

 resembles E. coli, but is distinguished by the formation of resistant cysts 

 containing four nuclei. In addition to these species, many others have 

 been described by various investigators for example, E. minuta, Elmassian, 

 which, according to Hartmann, is merely a variety of E. coli. A summary 

 of the various amoebae described from the human intestine is given by 

 Doflein (7) and Fantham (241). In Cochin China, Noc obtained from liver- 

 abscesses and dysenteric stools a small amoeba (not named) which in the 

 multiplicative phase reproduces in two ways : by binary fission of the ordinary 

 type ; and by budding off small amcebulae containing secondary nuclei formed 

 from chromidia. In the propagative phase Noc's amoeba encysts and breaks 

 up into amoebulae. Greig and Wells, in Bombay, obtained results very 

 similar to those of Noc. In cultures from liver- abscesses from Bombay, 

 Listen found two distinct forms of amoebae a larger form containing a single 

 nucleus and numerous chromidia, and a smaller form containing a nucleus 

 only. The larger amoeba multiplies either by binary fission, with karyo- 

 kinesis of the nucleus and partition of the chromidia ; or by the formation of 

 endogenous buds containing chromidia from which a secondary nucleus is 

 formed, the bud being finally set free as a small amoeba with a nucleus and a 

 number of chromidia. The small amoeba multiples only by binary fission, 

 preceded by amitotic division of the nucleus. Both large and small amoebae 

 form resting cysts, in which, however, they remain unchanged, and from 

 which they emerge when circumstances are favourable. It is evident that 

 much of the life-cycle of these liver-abscess amoebae remains to be worked out. 

 From, the foregoing it is clear that, with regard to the human pathogenic 

 amoebae, many important problems remain to be investigated, especially as 

 regards their specific distinctions, distribution, and life-history. Much 

 recent work has been carried on by culture -methods, with valuable results, 

 which, however, should be interpreted with caution, since it remains to be 

 ascertained whether the forms and phases assumed by these organisms in 

 cultures are identical in character with those which they exhibit under natural 

 conditions ; and until this point has been cleared up it is not safe to describe 

 the characters of a species of an amoeba, any more than of a trypanosome, 

 from cultural forms alone. 



With regard to the life-cycle of the pathogenic amoebae, it is most important to 

 discover what are the phases of development or conditions of life under which 

 they occur outside the human body ; whether they exist only in an encysted, 

 resting condition, or in an active state also ; and, in the latter case, whether as 

 free-living organisms or within some other host. On general grounds it is un- 

 likely that an organism adapted to an entozoic life should be capable also of 

 living free in Nature, and it is more probable that the pathogenic amoebae out- 

 side the human body occur only in the condition of resting cysts or spores, which 

 produce infection through being accidentally swallowed with food or water 

 (compare Walker, 276*5). In that case.unfiltered water, uncooked vegetables 



* Whether this also applies to cultures made from the pus of liver-abscesses, 

 as asserted by Whitmore (279) and Hartmann (247), may well be doubted ; it is 

 not easy to understand how an encysted amoeba could be transported passively 

 from the intestine into a liver-abscess. 



