64 PROTOZOAN PARASITISM 



at different locations here. At the bottom of the 

 crypts the amoebae appear to multiply, nests of 

 them may be seen, and here the epithelium undergoes 

 necrosis and dissolution, although in the upper part 

 of the gland it may be intact and apparently healthy. 

 Through the denuded base of the gland the amoebae 

 penetrate and move to the deeper tissues, traveling 

 through the lower tissues of the mucosa, the muscu- 

 laris, the submucosa, and possibly through the entire 

 wall. They spread laterally in the submucosa par- 

 ticularly, thus producing the characteristic lesion of 

 amoebic dysentery with undermined mucosa, which 

 may itself be more or less intact on the surface. 



The resistance to their advance offered by the host 

 is inflammatory locally. That there may be a hu- 

 moral antagonism is indicated by Craig's (1928) 

 complement fixation and Wagener's (1924) precipi- 

 tin experiments. 



The local inflammation includes congestion, ex- 

 udation of plasma, infiltration of mononuclear leuco- 

 cytes and proliferation of fibrous tissue. After ex- 

 posure of ulcerated tissue to the intestinal bacteria 

 the picture becomes confused by reaction against 

 such infection. 



The cytolytic activity of the amoebae is not con- 

 spicuous as a rule. As the parasites advance through 

 the tissues, they may be seen rather far afield, where 

 there is little evidence of tissue destruction or reac- 

 tion. The necrosis and ulceration occurs behind 

 them. Thrombosis of small blood vessels, which 



