62 
Philippine Journal of Science 
It seems not unlikely that, barring auto- or reinfection, the 
general run of lumen-dwelling parasites will seek new hosts and 
leave the original host in the course of a few years at the most. 
As for the tissue-dwelling parasites, we shall know better when 
we have means of ascertaining how they maintain their vitality 
over these long periods of time — just as we are seeking the solu- 
tion of the same problem with regard to the trypanosomes and the 
parasite of malaria. With Entamoeba histolytica, autogamy may 
occur periodically and solve the problem. In Balantidium coli we 
have a much more highly organized protozoon and one in which 
there is evidence of conjugation which, when it is fully worked 
out, may not be dissimilar to the process that has been so fully 
described in Paramoecium by Calkins and Cull. The conditions 
for conjugation would not seem to be especially favorable in the 
tissues, but in view of the extreme chronicity of Balantidium 
infections and the high type of the organism, and the fact that 
evidence of conjugation has never been observed in the tissues, 
it has long been the opinion of the senior author that endomixis 
may occur and be the means by which the virulence of the or- 
ganism is maintained. It is considered good form to regard 
protozoal infections as being especially virulent in children and 
young animals. In a general sense this is probably true, but 
the impressions we have gained, not only in connection with 
this series, but also from past observations, regarding Enta- 
moeba histolytica and Balantidium coli in connection v/ith 
children, incline us to the belief that certain things have been 
overlooked in the past. 
These are some of the biological factors involved, but the main 
factor of practical application would seem to lie in the personal 
equation — a purely social element. The public schools, visiting 
nurses, and physicians in Government and private practice will 
have to shoulder the responsibility in dealing with this very 
real menace — subtle no less than real. Work along the lines 
of general sanitation should be pushed with renewed vigor, but 
the keynote lies in the application of the principles of personal 
and household sanitation and hygiene that are apt to elude the 
sanitary inspectors. That means an educational campaign, vig- 
orous and long-sustained. Work of this kind has been under- 
taken more or less successfully against hookworm and malaria, 
but it should be stretched to include everything else. It might 
be remarked that almost every parasite carries its own little 
individual problem in relation to transmission. 
Epigrammatically expressed, we might regard the presence 
