AVENUES OF INFECTION 33 



ual. Two infections may occur simultaneously, each preserving 

 separate characteristics, and perhaps aggravating each other. 



The avenue of infection and the tissues infected alter the type of 

 the disease exceedingly. Streptococci invading the tonsils cause 

 tonsillitis, but the same organisms entering the skin cause erysipelas 

 or phlegmons; or if the uterus is infected after the birth of a child 

 the disease is still different and more serious. If the tubercle bacilli 

 enter the skin they produce lupus; if swallowed they cause ulceration 

 of the bowels, and subsequently invade the peritoneum; if inhaled, 

 tuberculosis of the air passages, phthisis, or tubercular laryngitis 

 may follow. If cholera spirilla be injected into a vein of a guinea 

 pig, it may develop choleraic septicaemia; if they are injected into 

 the peritoneal cavity, a choleraic inflammation of the peritoneum is 

 produced, and not a septicaemia. Pneumococci if injected into a 

 vein cause a rapid septicaemia, or they may give rise to abscesses 

 anywhere in the body. Like streptococci, they may be the cause 

 of inflammation in any tissue, particularly serous membranes, and 

 show different clinical entities, according to the organs involved, and 

 the morbid anatomy and physiology produced. The fatality of a 

 bacterial infection varies with the avenue of inoculation: it is safer to 

 have a skin infection than a meningeal, or endocardial one, not only 

 from the likelihood of rapid toxin absorption, but from purely 

 mechanical damage, as pressure and interference with vital functions 

 by inflammatory products such as exudates, tubercles, serum and 

 pus. The injection of pneumococci under the skin of a dog has a 

 more rapidly fatal effect than when they are injected into a vein, 

 according to Klemperer. 



It seems practically proven now that tubercle bacilli may enter 

 the lung by way of the intestinal tract, but Ghon has lately shown 

 that tuberculosis in childhood usually starts as an infection directly 

 into the lung tissue by bacilli coming in with air. 



Local immunity to infection. There is evidently more resistance 

 offered by the liver against invasion than by the peritoneum. It is 

 not likely that a man would contract typhoid through skin infection, 

 3 



