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different aspect. In order-to find out the reason for this fact, I would 
deem it necessarj- to analyse, if possible, a 1 1 the factors that have, 
or may have, a share in bringing about the fact. The species of the 
parasite is one of them ; the species of the host is another. But 
there are others, and amongst these the local conditions for infection 
are to my mind a factor of the first practical importance. This factor 
has been completely overlooked by HOLCOMB when lie drew his 
conclusions, although its value is, so far as I have a judgment, fully 
recognised in modern epidemiology. Let us only assume it were 
possible to take one of the West Indian Islands, make its climatical 
and hydrographical conditions absolutely like those of Egypt, make 
the population (which is slightly infected with intestinal Bilharziosis) 
as dense as it is in tlie Nile Valley', make it live and work after the 
fashion of the Egyptian fellah, and then shut the Island off entirely 
from communication with the rest of the world ; I have little doubt 
what the statistics would say some ten or twenty years hence. 
Resuming now what has been said in this lengthy discussion, I 
must state that, of the evidence brought forward by Dr. Sambon in 
order to justify the creation of ‘ Sck. viansoni' \ i, the zoological 
proof is absolutely insufficient; 2, the anatomo-pathological proof 
does not stand any serious test ; and 3, the geographical proof is 
based upon a peculiarly one-sided interpretation of the literature. In 
all the evidence there is not the slightest detail which would really 
point to the existence of a distinct species in the West Indies and 
certain parts of Africa. It would be unwise on my part to go so far 
as to contend that such a species, or perhaps even several species, 
can not, altogether, exist. This is quite possible from the zoological 
point of view ; but, zoologically, there is no possible doubt either that 
this species, or these species, must produce the same two 
shapes of eggs as does the Sch. hcematobiu 7 n, or else our 
present information is wholly incorrect. If, therefore, Dr. Sambon 
wishes to maintain that there is an independent ‘ Sch. mansoni ’ in the 
countries above-mentioned, the entire proof of its existence still 
remains to be given. 
I cannot conclude this article without making some remarks of 
remonstrance with regard to another passage in Dr. Sambon’S paper 
‘On the Part played by Metazoan Parasites in Tropical Pathology.’ 
Speaking of the infection with Agchylostoma duodenale, he says that 
