a 
940 
(2) The percentage of infections is greater than it is in animals 
fed in the manner given under 1, if suspensions of cultures of amoebee 
are inoculated directly into the ceca of monkeys by hypodermic injec- 
tions, either after opening the abdominal cavity or by direct puncture 
through the abdominal wall. 
However, even by this meéthod ameebic ulceration does not always 
follow, the results being influenced by the same agencies which cause a 
variation in the feeding experiments. 
(3) Ameebic infection can be produced in monkeys by rectal injections 
of cultures of the organisms, but the results of this procedure are less 
certain than they are when either of the other two methods is employed. 
The study of the influences which govern these results has not brought 
satisfactory conclusions. 
We have practically abandoned experiments which depend upon in- 
troducing the organisms into the gastro-intestinal canal, because a more 
aceurate method, which we will presently describe, has been developed 
by us. In the intestine the conditions for the study of amoebic or other 
infections are very complex and show little beyond the proof that amoebic 
ulcers may be produced by the introduction of cultures of the protozoa ; 
therefore, experimentation on other organs of the body serves more easily 
to solve the question of the pathogenicity or non-pathogenicity of the 
organisms. ; 
Our work in specific regard to the intestine seems to have established 
the following: 
(a) Amcebe are the causative agents in certain infections of the 
bowel. 
(b) Bacteria play an important part in this process by furnishing 
symbioses for the ameebe during the establishment of a more genuine 
parasitism. 
(c) In many of these infections true parasitism probably is not 
reached in the bowel, for here, even in the amoebic ulcers, the bacteria 
still help in the formation of a symbiosis. In this respect bacteria may 
be considered to influence the fundamental etiological agent. Certain of 
the pathogenic bacteria which are in symbiosis with the ameebe must 
certainly also take a more active part in the etiology of the lesions. 
Combinations with this class of organisms usually influence the sympto- 
matology of the disease and they may always be recognized in the 
histological study of tissues taken from such cases. 
(d) It is also true that pathogenic bacteria which are not concerned in 
the ameebic symbiosis may enter the intestine and play a part in the 
subsequent course of the ameebic lesions, and therefore it is probable, 
although it is not proved, that the simplest and purest ameebic lesion of 
the bowel is one where pathogenic organisms are not present and in 
which the bacterial symbiosis takes place with a non-pathogenic bacterium. 
