154 INFECTIOUS AND PARASITIC DISEASES. 



few infections in which the agents do not pass to the 

 exterior in a variety of ways. In those diseases which 

 are both local and general we find the most numerous 

 avenues of exit, and in them it is possible for the infec- 

 tious agent to leave the body in every one of the six 

 ways enumerated above. An example of a common 

 disease in which the germs make their exit in at least 

 five ways, with a possibility of six, is furnished by 

 typhoid fever; in its incipiency the bacilli are localized 

 in the lower portion of the small, and the beginning of 

 the large intestines — but they soon invade the blood, 

 and by the latter are so distributed that they may be 

 eliminated in any of the secretions, in localized sup- 

 purations, and even by the bites of insects. 



It often happens in the course of a disease that a 

 micro-organism will make its exit in some other way than 

 the channels ordinarily followed. This occurs princi- 

 pally when complications arise. Therefore, whenever, 

 in the course of an infectious disease, complications arise 

 in which there is a purulent or other discharge to the 

 exterior, these discharges should be regarded as fresh 

 avenues of exit for the specific micro-organisms. 



To be sure, complications are often due to microbes of 

 a species different from the one causing the primary 

 infection; but in the absence of definite information to 

 the contrary, it is a safe rule to regard complications 

 as due to a migration to another part of the body of 

 the first invader. Thus, when an otitis media (middle- 



