36 
The combined effect of the infections with Oxyuris and hookworms 
would tend to make the rate of infection slightly higher among patients 
of a long and of a short institutional life than among patients of an 
intermediate length of hospital life, as follows: 
Years. 
Examined. 
Infections. 
Per 100 
persons. 
Under 1 
626 
14 
2.24 
1 to 3 
858 
20 
2.33 
4 to 8 
737 
14 
1.90 
9 to 15 
445 
12 
2.70 
Over 15 
585 
13 
2.22 
The number of infections with these two worms was too small, 
however, to account in an } 7 considerable degree for the similar varia- 
tion in the frequency of total infections at different periods of hospital 
residence, the rates of total infection being governed largely by the 
relatively high number of infections with whipworms. 
SIGNIFICANCE OF INSTITUTIONAL LIFE AS A FACTOR IN THE 
PREVALENCE OF INTESTINAL WORMS. 
The peculiar result brought out above, namely, a decrease in the 
rate of infection for a certain length of institutional life and a subse- 
quent increase, may be accounted for in a small measure by the com- 
bined rates of infection with Oxyuris and hookworms, but in a much 
greater degree by the Trichuris infections. We have not been able 
to explain this peculiar variation in a manner mathematically exact, 
but certain considerations, as set forth in the following paragraphs, 
offer at least a possible explanation. 
Upon admission to the hospital, the patients would naturally have 
a given amount of infection, greater or less, according to the prevalence 
of intestinal worms under the conditions and among the population 
from which the patients came. These infections would, of themselves, 
tend to die out upon removal from the source of infection and in the 
absence of a new source resident within the hospital itself; this dis- 
appearance of the parasites would be more or less rapid according to 
the longevity of the worms, the amount of anthelmintic and purgative 
treatment to which the patients were subjected, and to the degree of 
resistance of the parasites to such treatment. 
It may be assumed, however, that there is among the patients of 
ever } 7 institution, as in the population at large, a given amount of 
endemic helminthiasis. Furthermore, it seems probable that in a 
long-established institution this amount of infection with intestinal 
worms would be fairly constant — that is, it would be the amount which T 
the sanitary and other conditions in the institution will support and 
propagate. 
