29 
cussed under the following heading, may have played a part in pro- 
ducing the difference which appears in our results between the preva- 
lence of intestinal worms at different ages among males and among 
females. 
SIGNIFICANCE OF SEX AND OF AGE AS FACTORS IN THE PREVA- 
LENCE OF INTESTINAL WORMS. 
Sex. — It may be pointed out that the present statistics are gov- 
erned chiefly by whipworms, namely, by a parasite which does not 
require an intermediate host, but a worm which is spread by means of 
the feces. Were we dealing with infections for which an intermediate 
host is necessary, as, for instance, liver fluke disease caused by Opis- 
thorchis sinensis , lung fluke disease caused by Paragonimus westermanii, 
or infection with Txnia saginata, contracted by eating beef, the sta- 
tistics would be influenced by the relatively greater intimacy between 
either sex and the source of infection. This same general principle 
ought to obtain in reference to parasites spread by eggs in the feces, 
but not requiring an intermediate host. 
In localities, such as rural districts, not provided with a sewage 
system, there is naturally as a rule a greater amount of human fecal 
matter to the square meter within a radius of 50 meters of a dwelling 
than there is in the fields. In average daily life females would in 
general be more closely confined to the area surrounding the house 
than would males. Accordingly, the natural inference would seem to 
be that all other things being equal, under conditions as above stated, 
females should show a greater infection with parasites, as hookworms 
and whipworms, which are spread by means of the feces without 
intermediate host, than would males. 
In the case of mining districts and excavations, more particularly if 
the houses are provided with properly kept privies, or in other districts 
where the fecal matter around the house is properly disposed of, the 
conditions would naturally be different and we should not expect to 
find this same relation between the amounts of infection in the two 
sexes. 
Thus it is seen that the relative frequency of helminthiasis among 
males and females may vary according to the species of parasite with 
which we are dealing, and even with one and the same species, the 
frequency may vary according to the environment; in particular, 
according to the relative intimacy of the sex in question with the 
greater concentration of infectious material. 
Stating this proposition in another way, it may be said that, while 
the existence of a physiological predisposition on the part of females 
can not at present be absolutely excluded, the relative frequency of a 
given parasite, or of helminthiasis in general, among males and 
females is apparently not so much a question of physiological predis- 
