THE PATHOGENIC PROTOZOA 281 



infrequently happens that such abscesses rupture through the 

 diaphragm into the lungs or into the peritoneal cavity. 



E. histolytica has been shown to be pathogenic for cats, dogs, 

 and monkeys, provided infection takes place either by feeding 

 them with material containing cysts or by rectal inoculation of 

 vegetative forms. 



The source of pathogenic amebic infection is not definitely 

 known. In Manila the water supply is considered responsible for 

 its transmission. Recent experiments on Filipinos who acted as 

 volunteers tend to show that E. histolytica is a strict parasite, 

 and consequently infection can only come from an individual 

 harboring the organism in the intestines. Since the organism 

 always enters the body by the mouth and leaves in the feces, trans- 

 mission evidently occurs through the ingestion of substances 

 contaminated with infected excretions. 



Examination of Feces. In fresh specimens E. histolytica ap- 

 pears as a large, round or oval body 20 to 30 /x in diameter ; the 

 nucleus is pale and not readily seen. Usually there are numerous 

 digestive vacuoles in which red blood cells may be seen. Often 

 in unstained preparations the amebse appear to be of a greenish 

 color, due, it is thought, to the hemoglobin liberated from the 

 ingested red cells. When in the cyst form they are small and round 

 and show four distinct spherical nuclei. 



The feces from a suspected case should be examined as soon 

 as possible after being passed ; a loopful of the slimy portion is 

 diluted with physiological salt solution and examined in a hanging 

 drop, preferably on a warm stage. By this means the kind of move- 

 ment and the nature of the vacuoles may be observed. The addi- 

 tion of a drop of 1 to 500 neutral red solution will stain the amebse 

 a pale pink color. 



Cultivation. After many unsuccessful attempts to cultivate 

 amebse, Musgrave and Clegg devised the following ingenious 

 method. Agar medium was poured into sterile Petri dishes, and 

 after hardening several rings of a pure culture of dead bacteria 

 were spread around the medium. A loopful of the material con- 

 taining the amebse was placed in the center of the dish. It was 



