ENTAMOEBA HISTOLYTICA 49 



shape may take almost any form — bulgings, constrictions, and various 

 distortions — so that they are difficult to describe. In general they are 

 similar to the irregularities so frequently encountered in the cysts of 

 /. biitschlii (cf. text-fig. 2, p. 115). 1 have seen pear-shaped, rod-shaped, 

 hourglass-shaped, L-shaped, and variously shaped cysts of other forms, 

 including many which are rhomboidal or triangular in outline. I have 

 twice seen " twin " cysts, formed of two complete cysts united at their 

 point of contact, and with their contents completely continuous. 



Nuclear abnormalities are not uncommon. Cysts containing three 

 nuclei — one large and two small — or nuclei of different sizes and 

 abnormal shape or structure may often be found. 



Do the Cysts of E. histolytica ever contain more than Four Nuclei f — As 

 a rule the cysts of E. histolytica contain, when mature, four nuclei. At 

 this stage development ceases. Some workers, however, believe that 

 occasionally all the nuclei again divide, so that a cyst containing eight 

 riuclei is finally formed. No worker claims to have observed more than 

 eight nuclei in a cyst of this species : but as this number is that 

 characteristic of E. coli, which so frequently accompanies E. histolytica, 

 it is of some importance to ascertain whether the latter species ever 

 produces similar cysts. 



Kuenen and Swellengrebel (191 3) claimed to have found cysts of 

 E. histolytica containing 5, 6, and 8 nuclei, and this was reasserted later 

 by Swellengrebel and Schiess (1917). The evidence adduced is, 

 however, most unconvincing : and I think it more than probable that 

 these authors mistook small cysts of E. coli, occurring in a mixed 

 infection, for those of E. histolytica. Kuenen and Swellengrebel (1913) 

 state that E. coli occurs " only seldom " in Deli, where they worked. 

 This can hardly be correct, for £. coli is so common everywhere else ; 

 but it implies — to my mind — that they overlooked or misinterpreted 

 many E. coli infections. Again, they cite a case in which the 8-nucleate 

 cysts of E. histolytica were found in company with " uiinnia " amoebae 

 of this species containing bacteria and starch grains. Now the pre- 

 cystic amoebae of E. histolytica do not eat either of these things, but 

 small E. coli amoebae, which are easily mistaken for them, frequently 

 do. I have no doubt that their patient was really infected with E. coli, on 

 this evidence alone. Further, these authors give 16 /a as the minimum 

 diameter of the cysts of E. coli, and they evidently reckoned all cysts 

 with a smaller diameter as belonging to E. histolytica — a very common 

 mistake : yet typical 8-nucleate cysts, undoubtedly belonging to E. coli, 

 may be found with considerably smaller diameters — at least down to 

 II /i. Another point which requires notice is their statement that 

 the 8-nucleate cysts of E. histolytica which they found " must " have 

 belonged to this species because the cyst walls showed only a " single 

 contour." This, as already noted,* is an incorrect statement about 

 either species, and rests upon an error in observation. It seems to me 

 certain, therefore, that Kuenen and Swellengrebel were mistaken, and 

 that their 8-nucleate " cysts of E. histolytica " were really in every case 

 cysts of E. colLj- 



Brug (1917 b) also believes that he has seen at least one cyst of 



* See p. 47, footnote. 



t The structure of the nuclei within these cysts is not described, though this is the 

 chief character by which a correct specific determination can be made. 

 4 



