50 THE AMOEBAE LIVING IN MAN 



E. histolytica containing 8 nuclei. His evidence is fairly strong, but is 

 not completely convincing, as Smith (191 8) has already pointed out ; 

 for he has not excluded the possibility of a mixed infection. He does 

 not say how often he examined the stools of his patient : he merely 

 states that they were " often " examined, and that E. coli cysts were 

 " always absolutely absent" — a very rash statement to make about any 

 stool. He does not sufficiently appreciate, apparently, the fact that 

 the stools of a person infected with E. coli may be examined on scores 

 of occasions without the infection being detected.* The 8-nucleate cyst 

 which he found measured 12^ in diameter: but imdoubted cysts of 

 E. coli also occur of this size. The cytological characters of the nuclei 

 are not given, and without knowing these it is impossible to be 

 absolutely certain of the species to which his cyst belonged.f 



Mathis and Mercier (1917 b) deny that E. histolytica ever forms cysts 

 with more than four nuclei. Most other workers who have had a very 

 large experience are also extremely doubtful regarding their occurrence : 

 and there can be no doubt whatever that, if they do occur, they are 

 excessively rare.t I have examined some hundreds of thousands of 

 cysts of E. histolytica, and I have seen but three which I believe to have 

 been 8-nucleate cysts of this species. That this interpretation is correct, 

 I am unable to prove conclusively, on account of the great difficulty — 

 amounting in practice almost to an impossibility — of excluding a con- 

 comitant infection with E. coli. I have not yet succeeded in finding 

 an 8-nucleate cyst of E. histolytica in my stained preparations ;§ and 

 the cytological details, especially as regards the finer nuclear structure, 

 cannot be made out with complete certainty in iodine solution — the 

 medium in which my cysts were examined. 



It seems almost certain, however, although the evidence so far is 

 inconclusive, that 8-nucleate cysts of E. histolytica must occur. All the 

 other cyst-forming amoebae of man occasionally form supernucleate 

 cysts, containing a double number of nuclei. Cysts of E. coli with 

 16 nuclei are not excessively rare ; 8-nucleate cysts of E. nana also 

 occur : and binucleate cysts of /. biitschlii may, on very rare occasions, 

 be found. Of the related amoebae in other animals, E. ranarum — 

 whose 4-nucleate cysts are very closely similar to those of E. histolytica 

 — very rarely forms 8-nucleate cysts, according to Epstein and Ilovaiski 

 (1914). I have never seen cysts with more than 4 nuclei in this species 

 (cf. Dobell, 1909), although I have now studied a considerable number. 

 £. aulastomi, another entamoeba with 4-nucleate cysts very like those of 

 E. histolytica and E. ranarum, also very rarely forms 8-nucleate cysts : 

 for Noller (191 2), who discovered this species, once found a single cyst 

 with 8-nuclei. In all these organisms there is little chance of the cysts 



* For some important data bearing on this subject see my earlier work (1917), and 

 also compare Smith (1918). 



t Brug does not use the "single contour" of the cyst wall as a specific character, 

 but for the singular reason that only a "single contour" is observable in the cysts of 

 both E, coli and E. histolytica ! 



X Vide Wenyon and O'Connor (1917), Dobell and Jepps (1917). 



§ I have, however, seen a stained cyst in a preparation made from one of my cases 

 by Miss Jepps : and from the cytological characters of this cyst, and the history of 

 the patient from whom it came — a patient whom I examined many times — I have 

 little doubt that it is an 8-nucleate cyst ol E. histolytica, and not oi E. coli. 



