THREE NEW AMERICAN CASES OE INEECTION OE MAN WITH HORSE-HAIR 
WORMS (SPECIES PARAGORDIUS VARIUS), WITH SUMMARY 
OE ALL CASES REPORTED TO DATE. 
By Ch. Wardell Stiles, Ph, D., 
Chief of Division of Zoology, Hygienic Laboratory, U. S. Public Health and Manne- 
Hospital Service. 
(Figs. 35-55.) 
There is a popular belief, extending back for centuries, that horse- 
hair worms ^Gordiidde)^ if swallowed bj man or animals, wdll cause 
very serious, even fatal, disease; but the actual cases of such infections 
thus far definitely recorded in medical and zoological literature are but 
few in number; and medical men who have reported cases do not share 
the belief of the laity relative to the supposed dangerous character of 
these worms. 
In recent 3^ears I have had specimens from two such cases referred 
to me for identification, and have seen another specimen from an unpub- 
lished case, and this has led me to consult the original references of all 
reported cases, so far as the literature is accessible to me. 
The worm.s in question belong to the Gordiacea^ a group of worms 
classified by some authors as a family of nematodes, b}" others as a dis- 
tinct order of the NematKelmintlies. Their general relations to the 
other round worms may be seen from the following key: 
KEY TO THE ORDERS OF NEMATHELMIXTHES. 
[For forms known to occur in man in the United States, follow roman tj’pe.] 
1. Anterior end provided with a proboscis, armed with several rows of thorns or hooks; 
intestine absent; adults parasitic in intestine; very rare in man; thorn-headed 
ivorms Acanthocephala 
Anterior end not provided with a thorny proboscis; intestine present, complete 
or in part rudimentary 2 
2. Intestinal canal of adult usually complete, but in some cases {Mermithidx) repre- 
sented by esophagus and rudimentary intestine; papillae on head; spicules 
usually present in male; one testicle present in male; vulva always inde- 
pendent of anus except in Cloacina; most round worm parasites of man belong 
here *. Nematoda 
Intestinal canal always atrophied anteriorly in adult; head without papillae; spic- 
ules never present in male; two testicles present in male; vulva always united 
with posterior portion of intestine to form a cloaca; rare in man and then only 
as accidental parasites; horse-hair worms Gordiacea 
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