78 Infection 



The avenue of entrance not only may determine that 

 infection is possible, or impossible, but may also determine 

 the form that it takes. This is well exemplified in tubercu- 

 losis. Tubercle bacilli rubbed into the deeper layer of the 

 skin produce a chronic inflammatory disease, called lupus, 

 that lasts for years and rarely results in generalized tubercu- 

 losis. Bacilli reaching the cervical or other lymph nodes by 

 entrance through the tonsils, may remain localized, produc- 

 ing enlargement and softening of the nodes, or passing 

 through them reach the circulation, in which they may be 

 carried to the bones and joints and occasion chronic in- 

 flammation with necrosis and ultimate evacuation or exfolia- 

 tion of the diseased mass, after which the patient may 

 recover. Bacilli entering the intestine in many cases pro- 

 duce implantation lesions in the intestinal walls; bacilli 

 inhaled into the lung, or conveyed to it from the intestine 

 by the thoracic duct and veins, produce the ordinary pul- 

 monary tuberculosis known as phthisis or consumption. 



Pneumococci colonizing in the pharynx have been known 

 to produce pseudomembranous angina; in the lungs, pneu- 

 monia; in the meninges, meningitis; in the cardiac valves, 

 endocarditis; on the conjunctiva, conjunctivitis. In all of 

 these cases we can look upon the type of infection as depend- 

 ing largely upon the portal through which the invading or- 

 ganism found its way into the tissues. 



The avenue of entrance is, for obvious reasons, less im- 

 portant when the micro-organism is of the rapidly invasive 

 form whose chief operation is in the streaming blood or in 

 the lymphatics. Anthrax in most animals is characterized 

 by a bacteremia regardless of the point of primary infection. 

 Bubonic plague rapidly becomes a bacteremia regardless of 

 the entrance of the Bacillus pestis by inhalation into the 

 lungs, or by way of the lymphatics through superficial lesions. 



It is not always possible to explain why certain channels 

 should seem so much more appropriate for infection than 

 others. When they are introduced beneath the skin, 

 bacteria are, in most cases, delayed in reaching the circula- 

 tion, and are in the meantime subjected to the action of the 

 various defensive mechanisms prepared for their destruction. 

 Many succumb to these after a time and never penetrate 

 more deeply into the body. Others are transported to the 

 lymph nodes, where they are destroyed, or, passing through 

 these and succeeding in reaching the venous channels, 



