56 Philippine Journal of Science 1920 
a little difference in the degree of incidence in various localities. 
These differences seem to be quite explainable on the basis of 
local conditions. For instance, in Cagayan Valley,, Willets 
found an incidence of hookworm infection in children under 1 
year of 5 per cent, with a steady increase with age until an in- 
cidence of 62.22 per cent is recorded by him for children between 
the ages of 10 and 14 years. This, Willets believes, is due to 
conditions in the tobacco fields that are peculiarly favorable to 
the development of the larve. We are inclined to suspect that 
a large proportion of the infections in children under 1 year and 
in children residing in the city of Manila are orally contracted. 
“Ground itch” is frequently reported in our out-door dispensary 
service, but we are reluctant at this time to attribute more than 
a smail proportion of the cases to hookworm invasion. Garcia 
reports an incidence of 14.28 per cent in his series of Cebu 
children; Garrison and Llamas report 11 per cent in children. 
These figures group rather closely around our figure of 12 per 
cent. 
The general impression in the Philippines among physicians 
and laboratory workers is that the hookworm is not nearly so 
dangerous a parasite to the Filipinos as it is to other people. 
We are not yet convinced of the entire truth of that impression; 
but, at the same time, we do not consider this series justifies 
us in arguing the point at present. Apparently the incidence 
of hookworm is greater in adults than it is in children. As an 
instance of this, one of us,(29) in a recent study of nine cases of 
dysentery in adult Filipinos, found the ova of Ancylostoma 
duodenale in six of them, which is in harmony with his routine 
observations. 
Many of these infections are exceedingly light and are diag- 
nosed only on centrifugation, while others are so heavy as to 
yield a diagnosis on direct examination of the feces. We are 
quite willing to admit that in a large proportion of cases in 
children and adults the symptoms are exceedingly mild, but 
we have seen cases in Filipinos that in every way presented the 
picture characteristic of severe hookworm infection. 
This modification of the symptoms in Filipinos has been ex- 
plained in two ways. Gomez,(24) who made a clinical study of 
hookworm infection in the Philippines, doubts that it can be 
explained on the basis of racial immunity. He inclines to the 
belief that a prevailing lightness of infection is the determining 
factor. Other observers adopt the suggestion made by Stiles 
and others that racial immunity may exist. In this connection 
