AMOEBA OF THE INTESTINAL TRACT. 103 



Reproduction within a cyst occurs when conditions 

 become unfavorable to vegetative existence. In 

 freshly voided specimens of f eces this process is very 

 rarely observed, but in specimens which have been 

 kept for some time this method of reproduction may 

 be easily studied. If the infection has existed for 

 some time encysted forms are more frequently ob- 

 served in the freshly voided feces, for, like many 

 other protozoan organisms, these parasites multiply 

 for a long period of time asexually, but after a cer- 

 tain number of generations the process of reproduc- 

 tion assumes a sexual character, self-fertilization 

 occurring within a cyst. 



The cysts of Entamoeba coli are spherical or oval 

 bodies measuring from 10 to 15 microns in diameter, 

 as a rule. The appearance of the cyst wall varies in 

 different stages of development, but it is always re- 

 fractile and generally presents a double outline. A 

 mammillated cyst wall is sometimes noted, but is by no 

 means commonly observed. 



Just before encystment the amoeba becomes per- 

 fectly motionless, while the endoplasm clears itself of 

 granular material and all foreign particles. This 

 process reduces the size of the organism about one- 

 third, and after it is complete there forms upon the 

 surface a very refractile, delicate, hyaline membrane 

 which appears to be formed from the substance of 



