148 Coccidia parasitic in man 
systematic foundation. The pages which follow embody my attempts in this 
direction. 
I have recently been able to read, or re-read, almost all the works dealing 
with the coccidia of man. This has been no small task, for much of the litera¬ 
ture is difficult of access; and I infer, from what I have read, that most people 
who have previously handled this subject have been deterred by this difficulty 
from consulting many of the original works. It is therefore almost superfluous 
to add that much of our “knowledge” has hitherto consisted of garbled 
versions of original records eked out with a number of groundless text-book 
traditions. No excuse seems necessary, therefore, for publishing this attempt 
to sift the facts and ascertain the truth. 
Through the kindness of my friend Dr C. M. Wenyon (now Lieut.-Col., 
R.A.M.C.), I was able to see the coccidia which he described from man in 1915. 
Since then I have seen and studied one of his forms anew, and have found 
another and apparently unrecorded species which will be described later in 
the present memoir. As there has hitherto been much doubt regarding the 
relation of the human coccidia to those occurring in certain animals, I have 
also re-examined the species in question in order to supplement my knowledge 
of these organisms and to corroborate and check the opinions which I had 
reached, concerning the parasites of man, from my study of the literature and 
of the parasites themselves. 
My researches on the coccidia—begun in 1906, and continued intermittently 
ever since—have given me a fairly extensive acquaintance with the group as 
a whole, and with the works, both ancient and modern, dealing with them. 
Without this knowledge I could not have attempted the present revision, nor 
should I have been able to express an opinion, on certain matters, with a degree 
of confidence such as the reader may sometimes observe in the following pages. 
I have dealt with much of the previously recorded work on the coccidia of man 
in a very critical spirit, because I wish to show how little is really and rightly 
known about this interesting group of forms, and how large a field there is, in 
consequence, for the activities of future investigators. If the present work 
succeeds in unravelling some of the old tangles, and provides a clue for other 
workers, who have the opportunity, to follow up, it will have served its 
purpose. None can be more conscious than I am myself of its numerous 
shortcomings. 
To obtain the original works describing the coccidia of man, and those 
related to them, I have had to ransack many of the large libraries in London 
and elsewhere, and I take this opportunity of recording my indebtedness to 
the librarians who have everywhere aided me most willingly. It would be 
tedious to enumerate all the libraries 1 which I have made use of, and to thank 
1 For the benefit of others I should like to mention, however, that the works of Rivolta— 
which are of considerable systematic importance—have proved most troublesome to obtain; but 
I finally succeeded in discovering copies of them in the library of the Royal College of Veterinary 
Surgeons, and should like to express my thanks once more to the Secretary, Mr F. Bullock, who 
recently unearthed them and enabled me to study them there. 
