175 
interpret it, of Sch. hmnatobhwi is perfectly suf 5 cient to throw light 
on this difference also. 
Before advancing any further, and in order to avoid any misunder¬ 
standings, I will repeat that I do not ignore that what I have said 
with regard to the nature of the lateral-spined eggs, and what I am 
going to say hereafter with regard to the differences in the clinical 
aspect of the disease, is a ‘ theory,’ inasmuch as it has not yet been 
established by experimental proof. In the absence of such proof, 
the only thing the scientific man, desirous of advancing our know¬ 
ledge, can do, is to collect carefully as many isolated facts as may be 
obtainable; to separate those which are (presumably) essential from 
those which are (presumably) accidental, and to piece all of them 
together into a continuous train of events. This is what I have 
been endeavouring to do ; I cannot imagine that a theory thus built up 
can be wrong in its fundamentals. It must, of course, be incomplete, 
or may be erroneous in details. I have already pointed out that 
Bilharziosis, in its varying aspects, presents a peculiarly complex 
problem, both as regards its pathogeny and the biology of the 
parasite. I do not think that I am wrong when I say that the latter 
represents the basis of the former, especially so far as the develop¬ 
ment and the behaviour of the worm within the human body are 
concerned. When, with regard to this part, I have knowledge of a 
good number of details, I owe that to the kind collaboration of my 
colleagues of the Medical School and the Kasr el Aini Hospital, Dr. 
Elliot Smith, the Anatomist, Drs. Symmers (now of Queen’s 
College, Belfast) and FERGUSON, Pathologists, Dr. Madden and Mr. 
Fr. Milton, Surgeons, who have discussed with me the observa¬ 
tions they had occasion to make during their professional work, and 
have given me many a valuable hint as to details with which I am less 
familiar. A priori, the various observations might have been ex¬ 
plained in various ways, but the right explanation could only be one 
which fitted in with the biology of the parasite. Sch. hcemaiobium has 
thus far successfully resisted all attempts at revealing the secret of 
its development. Nevertheless, we know a number of facts which 
definitely settle certain details; as to others, all we can do at present 
is to accept what seems to be most probable. For me, everything 
>s probable as soon as it has been demonstrated in the nearest natural 
relatives of the Sch. hcemalobiinn, i.e., eitlier in other Schistosomes, or 
