Cercarial Dermatitis — Chu 
309 
infection in them. This variation in host 
susceptibility caused by a change in diet sug- 
gests that seemingly contradictory results 
from host experimental infections for bird 
schistosomes may be due to differences in the 
diets fed the experimental hosts by the 
various investigators. 
Substantial data, on the other hand, have 
accumulated during the past several decades 
regarding the bionomics of the intermediate 
hosts of the dermatitis-producing schisto- 
somes. These data are chiefly concerned with 
(1) the habits of the snails, such as their food 
requirements, reproductive rates, adaptation 
to surroundings, and association with other 
plant and animal life, (2) the environmental 
conditions such as changes in pH and salinity 
in water, variation in temperature and amount 
of sunlight, and (3) susceptibility of the 
other species of snails in the locality to infec- 
tion by the schistosome miracidia. This in- 
formation is essential for understanding the 
reasons why the disease exists in specific lo- 
calities. Many reports also indicate that an 
intimate association between the infected 
birds and the snail intermediate hosts is a 
necessity before cercarial dermatitis can be 
established as a "Disease of the Place.” 
For fresh-water snails, cultivation in the 
laboratory has not been a problem, but for 
marine snails, technics for their cultivation 
are yet to be developed. The bionomics of 
marine snails is a fascinating subject. Ed- 
mondson (1946) stated that: "A specimen of 
Littorina pintado remained attached to the 
plastered wall of the Marine Biological Lab- 
oratory, Honolulu, for nearly a year. When it 
was returned to sea water it regained its activ- 
ity in a few minutes.” Attempts are now being 
made to breed Littorina snails in our labora- 
tory for use in experimental work on 
schistosomes. 
The investigation of all phases concerned 
with marine cercarial dermatitis is indeed a 
green pasture for those who are interested in 
diseases associated with a marine environ- 
ment. We encourage investigators in the Pa- 
cific area to participate in this field of study. 
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