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OBSERVATIONS ON THE GEOGRAPHICAL AND 
ETHNOLOGICAL DISTRIBUTION OF HOOKWORMS 1 . 
By SAMUEL T. DARLING, 
Professor of Hygiene, Faculdade de Medicina e Cirurgia 
de Sao Paulo, Brazil. 
During the course of investigations, primarily directed to a study of the 
effects of hookworm infection on people in different parts of the tropics, I 
have been struck with the peculiar geographical and racial distribution of 
the two common species of hookworms infecting man, and with its bearing- 
on certain ethnological problems. 
The observations I have made, in so far as they are related to anthropo¬ 
logical questions, are as follows: The races of mankind, living in tropical and 
subtropical regions, are infested with one or more species of hookworms. In 
the migrations of these peoples the immigrants have carried their peculiar 
species of hookworms into regions occupied by people having a different 
worm-species-content, and by an examination of the intestinal worms of a 
people, the geographical and ethnic origin of their hosts can, within certain 
limits, be divined. I refer particularly to migrations within 35° N. and 30° S. 
latitudes, for when migrations are made into colder climates the hookworm 
infection is ultimately lost through inability of the embryos to persist during 
the phase of their life cycle spent in the soil. 
There exists the deepest ignorance in regard to the migrations of people 
that have taken place in prehistoric times and also in regard to those within 
historic times where no records have been left. 
But at present, in tropical countries, certain movements of populations 
are going on in response to a demand for agricultural labourers. 
Large numbers of Tamils and Malabaris have been recruited to Malaya 
to work on rubber estates. Thousands of Chinese go annually to the same 
country to work in the tin mines. A great many North Indians from Calcutta 
are being employed-under indenture in Fiji and British Guiana on cane and 
rice plantations, there is a Javanese colony in Dutch Guiana. Japanese are 
colonizing in the State of Sao Paulo, Brazil. 
The origin and movements of these people are well known. They have 
brought enormous numbers of hookworms into the countries where they are 
employed. A study of the worms expelled from these people as well as those 
1 This work for the most part was done under the auspices of the Britisli Colonial Ofiice 
and with the support of the Rockefeller Foundation. 
