C. Dobell 
175 
This form also is well defined and easily recognizable: but it appears to be 
far less common than the Isos for a. and, since its discovery, has apparently 
been found again in other cases by only one observer, Roche (1917). It will be 
dealt with in greater detail in the systematic section. 
Since the publication of Wenyon’s observations, I have found the oocysts 
of another human coccidial parasite in the faeces of a single individual. This 
organism, like the last-mentioned, is also an Eimeria —having a tetrasporic 
oocyst and dizoic spores. It differs considerably, however, from Wenyon’s 
parasite; the oocysts being much larger (36/x). and the spores long and pointed. 
I shall reserve a fuller description of it for the next section. I will merely note 
here that it is a well-defined and undoubtedly distinct form, specifically unlike 
any other Eimeria hitherto described. 
As in the case of the Isospora, so with the two species of Eimeria found in 
man, it has not been possible as yet to determine the precise site occupied by 
the parasites in the tissues of their host. It appears highly probable, never¬ 
theless, that they five in the epithelial cells of the mucous membrane of the 
small intestine. Wenyon’s Eimeria is, at all events, so similar to the species 
infecting the mouse, that it would be expected to have a similar habitat in its 
host. It is to be remembered that the liver and the large bowel are—if we 
consider the Coccidia generally—unusual sites of infection in vertebrates. 
Before I attempt to reconcile the observations made by Wenyon and later 
workers with the earlier researches and opinions of others, it will be well to 
recapitulate the facts recorded in the present section. At the same time 
I would emphasize a point of importance: namely, that our knowledge since 
1915 contains, for the first time, some definite facts. It is no longer merely a 
mass of fragmentary findings connected by conjecture. 
The conclusions which can be drawn from the most recent work are as 
follows: there are, in man, at least three different coccidia—one species of 
Isospora and two of Eimeria —whose oocysts are passed in the faeces of 
infected persons. All three are forms which, during their schizogonic and 
gametogonic stages, probably inhabit the epithelium of the small intestine. 
There is, at present, no reason to suppose that these species are not peculiar 
to man himself. 
D. Discussion and Conclusions. 
It is now possible, after our brief analysis of all the more important facts 
known about the coccidia of man, to attempt to reduce them to order: and 
I will therefore indicate how this can be done, and show how the more recently 
discovered facts can be reconciled with the conflicting statements and views 
which have hitherto been current. 
It will be recalled that in an earlier section (Part 1, A) we noted that the 
observations of the earlier workers indicated that there are at least two 
different coccidia parasitic in man—one probably an Isospora , inhabiting the 
intestine, the other an Eimeria , inhabiting the liver. In the last section (Part I, 
Parasitology xi 
12 
