176 
Coccidia parasitic in man 
C) we have just concluded that the facts more recently brought to light reveal 
the existence of at least three coccidia in man—one species of Isosjjora and 
two of Eimeria, all probably inhabiting the intestine. As regards the occur¬ 
rence of a species of Isospora in the intestine, therefore, the records are in 
agreement: and we need have no hesitation, I think, in concluding that 
Wenyon’s Isospora is probably identical with that originally discovered by 
Kjellberg (Virchow, 1860), and possibly the same as the parasite observed by 
Railliet and Lucet (1890). 
When we attempt to go beyond this, however, the uncertainties increase. 
Were the coccidia found by Eimer (1870) of the same species? It is impossible 
to decide with certainty, because we have no description of them. But the 
nomenclature turns upon this question, because Eimer’s coccidia were the 
first to receive a name—“ Cytospermium ” hominis (Rivolta, 1878). We must 
either retain this name, applying it to one of the forms now known, or else 
eliminate it altogether. When names are already in use, and can be applied 
without violence to known forms, it is, I submit, better to retain them than 
to replace them by new ones. In the present case, therefore, I propose, since 
I see no more acceptable solution of the problem, to identify Eimer’s parasites 
with those of Kjellberg; and to suppose that both were the same organism 
(Isospora) whose oocysts were subsequently studied by Railliet and Lucet, 
and by Wenyon and others. This coccidium appears to be by far the com¬ 
monest of those occurring in man: and if, therefore, Eimer, or anybody else, 
discovered a “coccidium"' of which nothing is known but the fact that it 
inhabited the gut, then it is.more likely to have been the Isospora than any 
other. If this solution be accepted—and for every reason I urge strongly that 
it should be—then the problems connected with the nomenclature of this 
organism are immediately simplified, and there is no necessity to introduce 
any new name. The parasite becomes Isospora hominis Rivolta, 1878, with a 
long list of synonyms, mostly due to incorrect determination of the species— 
a form which can always in the future be easily recognized. I shall adopt this 
view as that which involves the fewest difficulties and leads to least confusion. 
It should be noted here that if Rivolta’s name is rejected, on the grounds 
that the organisms (Eimer’s) to which he gave it are not identifiable, then the 
next name which must be considered is that of Railliet and Lucet (1891). They 
found what they believed to be an Isospora in human faeces, and named it 
provisionally I. higemina var. hominis. If we admit that the parasite was 
specifically distinct from I. higemina —as there is every reason to believe— 
then its name could be arrived at by elevating the variety to specific rank. 
The coccidium would accordingly be known as Isospora hominis Railliet et 
- Lucet, 1891. The chief difficulty involved in this procedure is, however, the 
same as that which we encountered in the case of Rivolta’s name—the diffi¬ 
culty of determining precisely to what organisms the name was applied. For 
it is far from certain that the structures which Railliet and Lucet (1890) dis¬ 
covered really were the oocysts of an Isospora, or even of a coccidium. Their 
