Pathogenesis 499 



and sometimes the kidneys, and other organs where they 

 may be found always aggregated in small clusters in properly 

 stained specimens. The occurrence of the bacilli in the 

 tissues in clumps or clusters may depend upon the presence 

 of agglutinating substances in the blood. 



Mallory * found the histologic lesions of typhoid fever to 

 be widespread throughout the body and not limited to the 

 Peyer's patches of the intestine, where they are most 

 evident. His conclusions regarding the pathogenesis of the 

 disease are briefly: "The typhoid bacillus produces a mild 

 diffusible toxin, partly within the intestinal tract, partly 

 within the blood and organs of the body. This toxin pro- 

 duces proliferation of the endothelial cells, which acquire 

 for a certain length of time malignant properties. The new- 

 formed cells are epithelioid in character, have irregular, 

 lightly staining, eccentrically situated nuclei, abundant, 

 sharply defined, acidophilic protoplasm, and are charac- 

 terized by marked phagocytic properties. These phago- 

 cytic cells are produced most abundantly along the line of 

 absorption from the intestinal tract, both in the lymphatic 

 apparatus and in the blood-vessels. They are also produced 

 by distribution of the toxin through the general circulation, 

 in greatest numbers where the circulation is slowest. Finally, 

 they are produced all over the body in the lymphatic spaces 

 and vessels by absorption of the toxin eliminated from the 

 blood-vessels. The swelling of the intestinal lymphoid tissue 

 of the mesenteric lymph-nodes and of the spleen is due 

 almost entirely to the formation of phagocytic cells. The 

 necrosis of the intestinal lymphoid tissue is accidental in 

 nature and is caused through occlusion of the veins and 

 capillaries by fibrinous thrombi, which owe their origin to 

 degeneration of phagocytic cells beneath the lining endo- 

 thelium of the vessels. Two varieties of focal lesions occur 

 in the liver: one consists of the formation of phagocytic cells 

 in the lymph-spaces and vessels around the portal vessels 

 under the action of the toxin absorbed by the lymphatics; 

 the other is due to obstruction of liver capillaries by phago- 

 cytic cells derived in small part from the lining endothe- 

 lium of the liver capillaries, but chiefly by embolism through 

 the portal circulation of cells originating from the endo- 

 thelium of the blood-vessels of the intestine and spleen. 

 The liver-cells lying between the occluded capillaries undergo 

 necrosis and disappear. Later the foci of cells degenerate 

 * "Journal of Experimental Medicine," vol. m, 1898, p. 611. 



