The Cardinal Conditions of Infection 99 



to take place through the urogenital system, the conjunctiva, ' 

 or the skin. 



The avenue of entrance not only determines infection, 

 but may also determine the form that it takes. Thus, 

 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 inflam- 

 mation 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. 



Inhaled pneumococci colonizing in the pharynx have been 

 known to produce pseudomembranous angina; in the lungs, 

 pneumonia ; implanted upon the conjunctiva, conjunctivitis. 

 Jn these cases we can look upon the type of infection as 

 depending upon the portal through which the invading 

 organism found its way into the tissues. 



The avenue of entrance is, for obvious reasons, less 

 important 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. The failure of the micro-organisms to colonize 

 successfully when introduced through inappropriate avenues 

 may be explained by a consideration of the local conditions 

 to which they are subjected. 



When they are introduced beneath the skin, bacteria are, 

 in most cases, delayed in reaching the circulation, and are 

 in the meantime subjected to the germicidal action of the 

 lymph and exposed to the attacks of phagocytes. Many 

 succumb to these and never penetrate more deeply into the 

 body. Should any survive, they may be transported to 



