214 The Philippine Journal of Science 1919 
tion of a trichomonad that ingests red blood corpuscles. Only 
second in importance to this is the question as to whether they 
are digested by the parasite or are only fortuitously taken up to 
be later expelled like non-nutritious matter or unaccustomed 
food taken in by many of the free-living species of protozoa. The 
faculty of food selection is a striking feature of the life acti- 
vities of many protozoa, both free-living and parasitic. Calkins, 
speaking in a rather happy vein of certain predatory forms 
says that they “seem to select their food with all the care of 
a gourmand.” With many forms “all is grist that comes to the 
mill” and then the process of selection may take place within 
the cytopharynx or possibly within the cytoplasm, the non- 
nutritious matter or the nutritious matter to which the animal 
is not adapted being rejected and cast back into the environment. 
Many species are known to thrive best on some particular 
species of bacteria to the exclusion of others; some will prey 
upon smaller protozoa of one species alone to the exclusion of 
all others, as in the case of Didiniwm nasutum which derives 
its sole nourishment from Paramecium caudatum, and the same 
principle probably applies to a certain extent in the parasitic 
species, and is expressed to a degree in the predilection of cer- 
tain species for certain organs or tissues where they find the 
food to which they have become adapted. Others may nourish 
themselves by one method under certain physical conditions, and 
by another when these conditions change. . From this viewpoint, 
therefore, the problem becomes one of the bionomics of this 
particular trichomonad; and, having in mind the not infrequent 
occurrence of mixed bacillary and protozoal dysentery, we are 
inclined to cast the dysenteric symptoms out of this discussion 
until we can make further observations. 
Erythrocytes may be said to constitute a fairly specialized 
diet, one that in the natural order of events might be expected 
to be indulged in only by an organism that is, to a certain 
extent, adapted to life in the tissues. The lumen-dwelling intes- 
tinal parasites are, for the most part, vegetarians. Those which 
can be shown to make a meal from blood corpuscles and to 
derive nourishment therefrom have become carnivores and im- 
mediately fall under suspicion of being likely to cause destruc- 
tion of tissues. The case has been pretty well proved against 
Entameba histolytica almost in this count alone to the extent 
that the presence of erythrocytes in the cytoplasm is of great 
diagnostic significance and now the burden of suspicion falls 
heavily on Pentatrichomonas. 
