16,1 Haughwout and Horrilleno: Intestinal Parasites 63 
of protozoan parasites as an expression of an immediate filth, 
where helminth infection possibly presents an index of a more 
remote and diffuse filth which is all the harder to deal v/ith from 
the sanitary viewpoint. 
Transmission. — Protozoan diseases of the intestine for the most 
part are cyst-borne. We express ourselves with this reservation 
for the reason that the problem attending encystation and the 
transmission of parasites of the trichomonad group is still un- 
settled in so far as the forms infesting man are concerned. Cysts 
may be carried by various means — food, water, flies, and, if the 
whole truth were known, probably by a fairly wide range of 
arthropod vectors. As a vehicle for the conveyance of protozoal 
diseases, with the possible exception of the species included in 
the group of “coccidia,” dust is probably a negligible factor, 
for the cysts of the entamoebae and probably the general run of 
intestinal flagellates are poorly adapted to resist desiccation, a 
fact that has been well established in the case of Entamoeba 
histolytica. It is to this that we attribute, in a large degree, 
the preponderance of helminthal over protozoal infections in 
this series. The cysts of E. histolytica are quickly killed by 
drying, which may explain in part the low incidence of entamoc- 
biasis in children. But, again, there seems little reason to be- 
lieve that the cysts of other intestinal protozoa, with the excep- 
tion of those mentioned, would behave very much differently. 
We have regarded Giardia as rather a rare parasite in Manila 
and were somewhat surprised at its incidence in this series. 
However, w'e have no basis for forming an opinion as to whether 
or not there is a tendency to a rise in the incidence. A large 
proportion of the cases of Giardia infection seen by the senior 
author during the past few years he has been able to trace 
to Chinese gardeners and, in some cases, to China. Whether 
rodents are responsible for any of the incidence in the Philip- 
pines we cannot say. The senior author has found very few 
Giardia infections in Manila rats. 
We have already spoken of the rarity of infections with Ba- 
lantidium coli among children. The problem seems to be some- 
what similar to that presented by Entamoeba histolytica, but 
certain conditions applicable to Balantidium would appear to 
lend support to our belief that some physiologic factor inherent in 
children operates to limit infections in them with the obligatory 
protozoan tissue parasites. 
Walker (53) seems to have established pretty definitely the 
identity of the balantidia of the pig and of man, and among 
