ILLUSTRATED KEY TO THE TREMATODE PARASITES 
OE MAN. 
By Ch. Wardell Stiles, Ph. D., Chief of Division of Zoology, Hygienic Laboratory, 
United States Public Health and iMarine-Hospital Service. 
INTRODUCTION. 
Upon several recent occasions the writer has been called upon for 
information in regard to the trematodes which are parasitic in man, 
and it is in response to such requests that the present paper is pub- 
lished. This key is offered not as an exhaustive treatment of the 
subject, but as a ready reference aid in clinical diagnosis. 
To the American physician the trematodes or flukes have been here- 
tofore chiefly matters of scientiflc interest, most men looking upon 
them as zoological curiosities. Hepatic distomatosis, caused by 
Fasciola hepatica and 7d magna^ is known to occur in cattle, particu- 
larly in the Southern States; F. hepatica is also found in sheep in 
various parts of the country, and it need not be surprising if isolated 
cases of infection with this parasite should be fonnd in man. About 
20 cases of hepatic distomatosis, caused by Opisthorchi.s sinensis^ have 
already been found in this country, and it is strange that the cases 
thus far seen are so few in number. Parasitic hemoptysis, caused by 
Paragonimiis u'estermanii, has been found in the United States in 
dogs, cats, and swine, and one (imported) case in man has recently 
been recognized in Portland, Oreg. Bilharziosis, caused by Schisto- 
soma heematohium^ has been found in this country upon at least three 
occasions, and it is also said to occur in Cuba and Porto Rico. Thus, 
for the American physician, trematode diseases are becoming some- 
thing more than a mere matter of curiosity, and their importance is 
increased by the fact that about 120,000 of our troops have been serv- 
ing in the Asiatic quarter of the globe, or, in other words, in a part 
of the world where maladies of trematode origin are more common 
than the}" are with us. Whether the return of these troops, together 
with the return of travelers from Asia, will result in making these 
diseases more or less common in man in the United States can not be 
definitely prophesied, but the indications are that Ave shall not entirely 
escape infection. It is diflicult to guard against the introduction of 
the parasites under consideration, and the question whether they will 
midtiply here depends primarily upon two factors, namely, first. 
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