I08 THE AMOEBAE LIVING IN MAN 



31, PI. II). And it is possible — and perhaps probable — that there are 

 different strains of this species which can, as in E. histolytica and E. coli, 

 be distinguished by the dimensions of their cysts. 



As a rule the mature cysts of E. nana contain only four nuclei. But 

 cysts containing eight nuclei are to be found (fig. 86, PI. V), though these 

 are very rare. Up to the present I have not seen more than a dozen 

 such cysts among very many thousands examined. Swellengrebel and 

 Mangkoe Winoto (1917) say that they have seen cysts containing five and 

 six nuclei, but I cannot confirm their observation, and from their figures 

 I doubt its accuracy. Cysts showing at first sight more than four 

 nuclei are often met with : but careful study of these shows generally 

 that the supernumerary "nuclei" are really deeply-stained "volutin" 

 granules, or that a single nucleus with a bipartite karyosome has been 

 counted as two nuclei. The same authors hint at a possible " autogamy " 

 within the cysts of E. nana, and at other nuclear phenomena. It is 

 certain, however, that such suggestions are unjustifiable, and that 

 development in the straightforward manner described above is the rule. 

 In all the thousands upon thousands of cysts of this organism that I 

 liave examined from hundreds of infections, there is not the slightest 

 indication of any nuclear phenomena beyond those which I have 

 described. 



Occasionally the cysts of E. nana contain peculiar inclusions 

 resembling rods or granules. They are sometimes long and filamentary 

 and sometimes in the form of definite bundles of short rods or heaps of 

 coccus-like granules. Two cysts with such inclusions are shown in figs, 

 28 and 29, PI. II. Those with filaments in them can be mistaken for 

 small cysts of lamblia {Giardia intestinalis) . The inclusions are visible 

 in the living cysts, and are well seen in those stained with iron- 

 haematoxylin ; but they are not easily distinguishable in cysts stained by 

 most other methods. Such cysts appear to be characteristic of the 

 infections in certain individuals. At all events, I have found that when 

 they are present in the stool of a given individual on one occasion, they 

 can be found again in his stools subsequently for a period of at least 

 several months. What these inclusions are I am unable to state. From 

 their forms one might suppose that they are parasitic or symbiotic 

 bacteria ; but they may possibly be structures comparable with the 

 cliromatoid bodies of E. histolytica and E. coli. 



Occnrrence. — E. nana is one of the commonest inhabitants of the 

 human bowel. Since the appearance of the work of Wenyon and 

 O'Connor it has been found by every competent worker who has made 

 a protozoological study of human stools. It occurs in the faeces of 

 persons who have never left the British Isles, and is plentiful among 

 British troops invalided to England from the tropics and from France. 

 There are now numerous records available showing its frequency (see,, 

 for example, Wenyon and O'Connor (1917), Dobell and Jepps (1917), 

 Mackinnon (1918), etc.). The cysts of this organism are small, and 

 easily overlooked. Consequently, the incidence of infection is higher 

 than would appear from most published records. A series of British 

 soldiers — 156 cases, consisting entirely of dysenteries from abroad, and 

 all infected with E. histolytica — which I examined (in conjunction with 

 Miss Jepps) with great care, in order to determine the exact incidence of 

 infection with this organism, showed that it was present in no less than 

 33 "3 per cent. Every case was examined at least seven times, and many 



