48 THE AMOEBAE LIVING IN MAN 



than at a low temperature. At body temperature they generally die 

 within a few days at most. Degeneration of the cysts is readily recog- 

 nizable. The nuclei first become unnaturally distinct in the fresh cysts 

 — owing to the coagulation which occurs on the death of the proto- 

 plasm — and then break up. As the cysts die they also become permeable 

 to aqueous solutions of various stains (eosin, etc.). The cytoplasm 

 becomes vacuolated, and finally disintegrates. 



Cysts are passed in the faeces in the uninucleate, binucleate, or 

 quadrinucleate stage. Those containing less than 4 nuclei never 

 develop to maturity outside the body, and usually die much sooner 

 than the mature cysts. Even cysts with dividing nuclei do not complete 

 their nuclear divisions. Spindle-figures and other stages arrested in 

 division can be seen to remain unchanged within the cysts until 

 degeneration takes place. 



Numerous observations on the vitality of the cysts have already 

 been recorded. (Cf. Kuenen and Swellengrebel (1913), Wenyon and 

 O'Connor (1917), etc.) My observations are in general agreement with 

 those of others, and with my earlier observations on the cysts of 

 E. ranarnni. 



Several common variations in the contents and form of the cysts 

 of £. histolytica must be noted. These concern chiefiy the chromatoid 

 bodies and the shape of the cyst as a whole. As regards the former, it 

 may be noted first that the chromatoids are sometimes formed in the 

 precystic amoebae before the cyst wall is secreted (see fig. 82, PI. V). 

 This is not very uncommon. Secondly, the chromatoid bodies show 

 considerable variation in form. Although typically few and in the form 

 of thick short rods, they may be very numerous (fig. 70, PI. IV) and of 

 many different shapes — long thin rods, filaments, round or irregular 

 masses, granules, etc. (Cf. figs.3-5, 70, 72-76.) Sometimes they are 

 completely absent (fig. 71) in cysts at all stages of development. 



Malins Smith (1918) has recently attempted to determine the 

 frequency with which chromatoid bodies occur in the cysts of £. histo- 

 lytica. He found that they were present in 27 per cent., absent in 

 65 per cent., and doubtful in 8 per cent, of 1162 cysts which he 

 examined. Unfortunately he did not take into account the fact that 

 the chromatoid bodies disappear gradually from the cysts after they 

 have left the body, and he does not state how long his cysts had been 

 kept before he examined them. Moreover, his figures are based upon 

 the study of living cysts in saline, or those examined in iodine solution* 

 — not upon stained specimens. It is certain that he would have 

 found a much higher percentage containing chromatoid bodies had he 

 examined only freshly-passed cysts in carefully stained preparations. 

 His figures can thus hardly be accepted as a correct estimate of the 

 frequency with which chromatoid bodies occur normally in the 

 development of the cysts of E. histolytica. 



Although the cysts of E. histolytica are typically fairly symmetrical, 

 they may have the most bizarre shapes. Slight irregularities in outline 

 are commonly seen, and occasionally an infected person will pass a 

 stool in which almost every cyst is irregular in shape. Abnormalities in 



* It should be noted that small chromatoid bodies — and sometimes even large ones 

 — are difficult to distinguish in cysts mounted in iodine solution. 



