456 INFECTION AND IMMUNITY. 



rarely extends below the submucosa. Such foci 

 are said to be the most marked in the descending 

 colon and sigmoid where mechanical injury is 

 more likely to occur. The necrotic areas separate 

 by sloughing, leaving superficial ulcers. The lym- 

 phoid follicles are swollen and infiltrated with 

 polymorphonuclear leucocytes, which also accumu- 

 late in the dilated lymph spaces of the intestinal 

 wall. The ileum is so commonly involved that the 

 condition is called an ileocolitis. Conspicuous 

 changes are not found in the mesenteric glands or 

 spleen. The liver and kidneys commonly show 

 parenchymatous degenerations. 



of The dysentery bacillus is highly toxic. Subcu- 

 t ane(ms injections of killed cultures produce in 

 man a more profound reaction than the organism 

 of either cholera or typhoid. Ordinary laboratory 

 animals are so susceptible that they are immunized 

 with difficulty; the horse is less susceptible. The 

 toxicity of the organism apparently depends on an 

 intracellular toxin (an endotoxin) rather than on 

 a soluble toxin. When living or killed cultures 

 are submitted to autodigestion in salt solution 

 (Conradi, Neisser and Shiga), or when bouillon 

 cultures are allowed to grow for 30 days, the 

 liquids are found to be toxic after the organisms 

 are removed. In both instances this toxicity prob- 

 ably depends on the liberation of endotoxins. The 

 question as to whether the bacillus in the intes- 

 tines produces a soluble toxin which is absorbed by 

 the lymphatics, is undetermined. It seems more 

 probable that the conditions are analogous to those 

 of cholera, intoxication resulting from the libera- 

 tion of endotoxins by the solvent action of the tis- 

 sue fluids or cells on the bacilli. Dysenteric symp- 



