15 
are predisposed® to infection with eelworms and dwarf tapeworms and 
(in a lesser degree) with hookworms; that pinworms and Cochin China 
worms are slightly more common among whites than among negroes. 
The indication of a predisposition® on the part of negroes to infec- 
tion with Hymenolepis nana is much strengthened by certain figures 
not brought out above, namely, that among the 2,129 adult white 
patients excluded from the above group by selecting patients admitted 
to the Government Hospital from the District of Columbia, there 
appeared only 1 infection wdth the dwarf tapeworm (0.05 infection 
per 100 persons), while among the 81 adult negroes so excluded this 
parasite gave 2 infections (2.47 infections per 100 persons). The 123 
children (white) examined at the orphanage, however, gave 4.88 per 
cent of infections with dwarf tapeworms, a rate considerably higher 
than that among adult negroes. This would seem to indicate simply 
that age is a more potent factor than race in determining the preva- 
lence of this worm. (For age in its relation to helminthiasis, see 
pp. 23, 30.) 
As stated in the introduction (p. 10), too much absolute importance 
must not be attached to the statistics for pinworms. As the con- 
traction and transmission of infections with this parasite are largely 
questions of personal cleanliness, we might expect the actual relative 
prevalence of pinworm infections in the two races to be directly oppo- 
site to that indicated in our results. 
With regard to the relative prevalence of hookworms among whites 
and among negroes in America, Stiles, in his report upon the preva- 
lence of hookworm disease in the Southern States (1903, 51-52), 
says that clinically he found the malady comparatively rare in the 
negro race, and he raised the question whether this may be due, as 
suggested by Zinn and Jacoby (1896, 13), not to a lower frequency of 
infection among negroes, but to the negroes being less susceptible to 
the effects of the poison produced by the worms. This observation 
and the explanation suggested are strikingly confirmed by certain 
data contained in the latest publication (1906, Jan. 1, 10-11) of the 
anemia commission in Porto Rico. Of 14,560 white patients who 
appeared at the clinics for uncinariasis, 72 + per cent presented types 
of the disease classified clinically either as medium, intense, or very 
intense cases, leaving only 27 + per cent of light and very light cases. 
Of 670 negro patients, however, only 41+ per cent presented the 
severer types of the disease, while 58+ per cent were classified as 
light or very light cases. On the other hand, considering the severity 
a By racial predisposition to helminthiasis on the part of negroes we do not mean to imply 
any special physiological susceptibility to infection with intestinal worms such as is supposed 
to be present in the negro with regard to smallpox. While such a physiological suscepti- 
bility is not at present excluded, it is highly probable that a predisposition to intestinal 
worms in negroes would consist largely in a greater exposure to infection, depending on per- 
sonal habits, environment, etc. __ 
