33 
In other words, the liability to infection as expressed in the per- 
centage of infected to the uninfected or to the whole number of any 
age period as found under similar conditions, is a more exact index 
of the probability of helminthiasis than is the number of cases treated 
for any given age. Still, for age periods between 10 and about 60 
years the statistics give a more exact indication of conditions than for 
age periods below 10 and over 60 years, since for the persons of middle 
age there is not the same difficulty attendant upon visiting the clinic 
as there is for the very young and the very old. 
When now it is considered that normally there is necessarily in anv 
aJ 
large area a greater number of children under 5 years of age than in 
any other 5-year period, also that women are more confined by the 
care of children under 5 years than of older children, and, further, 
that only 35 hookworm children under 5 years are given in the report 
as against 1,027 from 10 to 14 years, an additional argument is pre- 
sented for suspecting that the sex and age statistics given for Porto 
Rico are governed by other factors beside the relative liability to infec- 
tion presented by the two sexes or different ages. 
LENGTH OF INSTITUTIONAL LIFE. 
In considering the influence of institutional life upon the frequency 
of intestinal worms, we are confined to the patients examined at the 
two hospitals for the insane, since the necessary data were not 
obtained for the children at the orphanage. 
The results of our first 500 examinations seemed to indicate that 
the frequency of infection with intestinal worms tended to decrease 
as the duration of institutional life lengthened. The statistics 
obtained from our whole number of adult cases (3,334) modify these 
earlier indications in a rather complicated manner. 
Separating the patients examined according to their length of resi- 
dence in the hospitals, we have made five groups, namely, (1) patients 
with a residence of less than 1 year; (2) from 1 to 3 years; (3) from 
4 to 8 years; (4) from 9 to 15 years, and (5) of over 15 years. 
The rates of infection with all parasites in these various groups of 
patients, including all adult cases examined, 0 were as follows: 
Examined. 
Infections. 
Per 100 
persons. 
Total infections: 
Under 1 year 
626 
78 
12.46 
1 to 3 years 
858 
93 
10.84 
4 to 8 years 
737 
54 
7.33 
9 to 15 years 
445 
43 
9.66 
Over 15 years 
585 
76 
12.99 
a Exclusive of 83 patients whose length of residence in the hospital could not be ascer- 
tained. 
32004— No. 28—06 3 
