BACILLUS TYPHOSUS. 409 



as a true infection, caused by the introduction and 

 growth of typhoid bacilli. It belongs to that class of 

 infectious diseases which are known as metastatic that 

 is to say, diseases in which the specific bacilli do not 

 abound in the entire circulation, as in septicaemia, nor 

 remain localized in one place, but are distributed in 

 groups throughout the body. The characteristic lesions 

 of typhoid fever are seated in the lymphatic structures of 

 the intestine namely, the solitary follicles and patches 

 of Peyer, the mesenteric glands, and the spleen. The 

 liver and kidneys are less commonly attacked. Wher- 

 ever found the typhoid bacilli are observed to be arranged 

 in groups or foci; only occasionally, as in the walls of 

 the intestine, are they singly or loosely aggregated to- 

 gether. These foci are formed, most probably, during 

 life, as is proved by the degenerative changes often 

 seen about them; but it is possible that the bacilli may 

 also multiply somewhat after death. 



The production of the lymph-nodules so often found 

 in typhoid fever in the internal organs is due to the 

 effects of the toxic substances eliminated by the typhoid 

 bacilli. This hyperplasia is particularly evident in the 

 lymphatic structures of the intestine, these being more 

 directly under the influence of the concentrated products 

 of the bacilli. To these, however, other inflammatory 

 processes are added, until finally necrosis or sloughing 

 of the tissues takes place. Possibly all these series of 

 changes may be at times caused solely by the products 

 of the typhoid bacilli which are gathered at certain 

 points. There is no question, however, that usually 

 other organisms take part in the production of these 

 processes in the intestines, but it remains to be deter- 

 mined when they begin to do so. In typhoid fever 



