62 PROTOZOAN PARASITISM 



The contention of anything in the region of a con- 

 stant intestinal invasion in the very large number of 

 infected persons, if this itself is correct, remains to be 

 proven. 



The finding of an amoeba indistinguishable from 

 Endamoeha histolytica as, apparently, a lumen 

 dweller in the rat, must also be considered in an ar- 

 gument at the present. 



The amoeba does not encyst within the tissues but 

 this process occurs in the lumen as the organisms are 

 carried down with the intestinal content to the lower 

 bowel, where inspissation takes place. As they pro- 

 ceed to encystment they become smaller and less 

 active. As cysts they pass out with defecation to 

 become the form transmissible to a new host. 



It is not known whether they multiply in the colon 

 from their own cysts, that is, whether excystment 

 takes place here. Ordinarily at least it appears that 

 division of the trophozoites is the manner of increase 

 and that this occurs mainly in the lumen and in the 

 glands. 



The properties of the amoeba which enable it to 

 invade the tissue are its physical ability to squeeze 

 between adjoining cells and, particularly, its cytoly- 

 tic action upon cells with which it comes in contact 

 (Craig, 1928). James (1927) (Scientific exhibits, 

 Amer. Med. Ass'n) has shown that Endamoeha histo- 

 lytica is capable of pushing its way between the 

 epithelial cells of an intact mucosa. How common or 

 important this is it is impossible to say. In the 



