64 Philippine Journal of Science 1920 
other important points he has made is that which establishes 
the domestic pig as the chief source of human infections with 
Balantidium in the Philippine Islands. Furthermore, he has 
shown that a large proportion of the pigs in and about Manila 
(and there are many of them) are parasitized with Balantidium 
and are constantly passing the encysted forms of the parasite in 
their feces. Encysted forms rarely occur in human feces. The 
senior author confesses never to have seen encysted Balantidium 
in human feces; but Walker was fortunate enough to find them 
in one or two of his cases, which would appear to be added 
proof that Balantidium is not yet completely adapted to man 
and that the pig is, perforce, the main source of the infection. 
We cannot be absolutely certain that none of our children 
were infected with Balantidium; but, from the thoroughness 
with which our examinations were made, we think it unlikely 
that we missed any cases. Latency, however, is a prominent 
feature of Balantidium infections, and the parasites may be 
absent from the stools over long periods of time during which 
there will be a total absence of symptoms. Walker says this 
latency in man is due chiefly to the fact that the patient, al- 
though parasitized, is not infected with the parasite, but in part 
to the chronicity of the ulcerative process in infected cases. 
In a measure, the problem of infections with Balantidiwm is 
tied up with that of Ascaris; for, granting that Ascaris suum 
is identical with Ascaris lumbricoides, we may assume that the 
pig may serve as a source of infection with both organisms. 
That being the case, why do children whose daily life brings 
them into frequent contact with the ground that has been tra- 
versed by pigs, and often in more or less intimate contact with 
the pigs themselves, contract Ascaris infections and escape in- 
fections with Balantidium ? 
Of the helminths occurring in our series only one, Oxyuris 
(and that occurred in a solitary instance), is capable of direct 
transmission or auto-infection. Hookworms have in the past 
been thought to have a comparatively limited existence in their 
passage between hosts, but recent observations raise a doubt 
on this point. Ascaris and Trichuris ova are known to be long- 
lived and resistant to unfavorable conditions, and it seems likely 
that many cases are picked up by the children when they play 
about the dusty streets and roads. Carriage by flies has been 
proved, but we doubt if this is an important factor with the 
children—there are too many other better and more “convenient” 
opportunities. 
