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 septicemia, 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 
