C. Dobell 
149 
again individually all the friends who have, at one time and another, helped 
me to obtain works which are not readily accessible. I would ask them 
collectively, therefore, to accept again this expression of my gratitude. I am 
further beholden to several of my friends for information or assistance, which 
will be acknowledged in the proper place. I must, however, make special 
mention here of my indebtedness to Captain F. W. O’Connor, R.A.M.C., who 
when he found that I was engaged upon the present work—most magnani¬ 
mously placed at my disposal all his unpublished observations upon the 
Jsospora of man. They were naturally of great interest to me, and I have 
availed myself of his generosity to the extent of incorporating some of his 
results, with due acknowledgments, in my account of /. hominis (Part II, 
sect. 1). I gladly offer him my thanks again here for his unselfish action. 
I have only to add that I have completed the present work, and made most 
of the original observations recorded in it, whilst working with the aid of 
grants from the Medical Research Committee. Without this assistance, and 
0 
the experience and knowledge gained whilst working on their behalf, the work 
itself could certainly never have been undertaken. 
PART I. 
HISTORIC AND ANALYTIC. 
The history of our knowledge of the coccidia of man is difficult to write. 
It is complicated by the circumstance that our knowledge of the Coccidia, as 
a group, is comparatively recent 1 , whilst most of the original cases of human 
coccidiosis were recorded during the early period of ignorance and uncertainty, 
and usually by workers with very scanty knowledge of the organisms related 
to those which they described. The older accounts are thus frequently written 
in an archaic language which is not easily comprehended—or which is, at least, 
apt to be misunderstood—by a modern worker unversed in the history of this 
particular branch of protozoology. To add to the difficulties of exposition, the 
coccidia of man are related to, and have frequently been confounded with, 
those of other animals; and these latter coccidia are unfortunately among the 
species which have changed their names periodically. We have thus to cope 
not only with discrepancies and difficulties in matters of fact, as recorded by 
different observers, but also with a confusing change and interchange of names 
which has thrown the nomenclature of the entire group of species into a state 
of chaos. 
In considering the cases and findings already recorded, I have thought it 
best to divide my analysis into two distinct parts—one dealing with the work 
done prior to the year 1915,and comprising therefore all the older observations; 
the second dealing with the observations recorded from 1915 to the present 
day. I adopt this procedure because the year 1915, in which the observations 
1 The life-history of the coccidia, it may be recalled, was not properly understood until the 
publication of the celebrated researches of Schaudinn and Siedlecki in 1897. 
