46 THE AMOEBAE LIVING IN MAN 



prove nothing* in this respect, and all that can be said with certainty- 

 is that they appear in the cytoplasm, where they increase in size. When 

 fully developed they are most commonly in the form of a few fairly- 

 large blocks or bars with rounded ends (cf. Hgs. 3-5, PI. I). 



At the time when the chromatoid bodies make their appearance^ 

 a vacuole also forms in the cytoplasm (fig. 3). It is of variable size, and 

 sometimes two or even three are formed instead of one. The vacuole 

 is stained brown in iodine solution, but not so deeply as the corres- 

 ponding structure in the cysts of the other intestinal amoebae. In 

 iodine solution its edge is not as a rule sharply defined. The brown- 

 staining substance in the vacuole is glycogen ; for it not only gives the 

 iodine reaction just noted, but also shows the characteristic solubilities 

 of this substance, and can be stained by Best's specific carmine methodf 

 (fig. 6, PI. I). 



The cyst when first formed is uninucleate (fig. 3, PI. I). Its nucleus 

 typically measures about one third of the diameter of the whole cyst, or 

 slightly less. The nucleus later divides into two (fig. 4), and each of the 

 daughter nuclei then again divides, so that four nuclei are finally formed 

 (fig. 5). In this quadrinucleate stage the diameter of each nucleus is 

 approximately one sixth of that of the entire cyst, or about half that of 

 the nucleus in the uninucleate cyst. The nuclei of the binucleate cyst 

 are intermediate in size. (Cf. figs. 3, 4, and 5, PI. I, and figs. 72-76, PI. IV.) 

 The nuclear divisions within the cyst appear to be exactly like those in 

 the free amoebae, except for the progressive reduction in size. They are 

 also almost exactly like the nuclear divisions in the cysts of E. rananmi, 

 which I have elsewhere figured in detail (Dobell, 1909). At all stages in 

 development the resting nuclei in the cysts of E. histolytica have 

 a structure exactly like that seen in the free forms. It is therefore 

 unnecessary to describe it again. One noteworthy feature may be 

 mentioned, however. In 2-nucleate or 4-nucleate cysts, the nuclei often 

 show a characteristic condensation of chromatin at one pole, so that the 

 "ring" of chromatin appears slightly thickened at one side (see fig. 5). 

 This also I have described previously in E. ranarinn. 



When the cyst has reached the 4-nucleate condition, no further 

 nuclear divisions occur. The glycogen vacuole, however, generally 

 disappears, so that the mature cyst comes to stain uniformly pale brown 

 throughout in iodine solution. If the mature living cysts are kept under 

 observation, they can also be seen to lose their chromatoid bodies^ 



* James (1914) apparently believes that the chromatoid bodies must be cytoplasmic in 

 origin because they can be coloured blue by Mann's method. But they can also be 

 coloured red by this stain (cf. figs. 3-5, PI. I), and it is even possible to stain some blue 

 and some red in the same cyst. I have excellent specimens showing them blue, red, 

 and all intermediate shades of purple in the same preparation. 



t As first shown by Kuenen and Swellengrebel (1913). 



t Malins Smith (1918) has recently stated that "the supposition of some writers 

 (Hartmann, 1912, James, 1914) that chromatoid bodies tend to disappear as the cyst 

 becomes mature is not borne out by the facts." That the mature cysts, with 4 nuclei, 

 lose their chromatoids when kept outside the body, is, however, a fact. I first showed 

 this to occur in E. ranarum, and have since confirmed it repeatedly in E. histolytica. 

 It is also confirmed by Chatton {iqij b). If Smith means that the cysts do not lose their 

 chromatoids in developing from the uninucleate to the quadrinucleate stage, then he is 

 probably correct. Nobody has yet maintained that this occurs, however, so far as I am 

 aware. Smith appears to have misunderstood what Hartmann wrote— as reference to the 

 passage which he quotes from him seems to indicate. 



