412 APPLICATION OF METHODS OF BACTERIOLOGY 



Modes of Infection. Experimentally, tuberculosis may 

 be produced in susceptible animals by subcutaneous inocu- 

 lation, by direct injection into the circulation, by injection 

 into the peritoneal cavity, by feeding of tuberculous material, 

 by the introduction of the bacilli into the air-passages, and 

 by inoculation into the anterior chamber of the eye. 



In the numan subject the most common portals of infec- 

 tion are, doubtless, the air-passages, the alimentary tract, 

 and cutaneous wounds. When introduced subcutaneously 

 the resulting process finds its most pronounced expression 

 in the lymphatic system. The growing bacilli make their 

 way into the lymphatic spaces of the loose cellular tissue, 

 are taken up in the lymph-stream and deposited in the 

 neighboring lymphatic glands. Here they may remain and 

 give rise to no alteration other than that seen in the glands 

 themselves; or they may pass on, to neighboring glands, 

 and eventually be disseminated throughout the lymphatic 

 system, ultimately reaching the vascular system. 



Having gained access to the bloodvessels the results are 

 the same as those following intravascular injection of the 

 bacilli, namely, general tuberculosis quickly follows, with 

 the production of miliary tubercles most conspicuous in 

 the lungs and kidneys; less numerous in the spleen, liver, 

 and bone-marrow. 



When inhaled into the lungs, if conditions are favorable, 

 multiplication of the bacilli quickly occurs. Coincident 

 with their growth they are mechanically pressed into the 

 tissues of the lungs. As multiplication continues some are 

 transported from the primary site of infection to healthy 

 portions of the lung-tissue, where, through their develop- 

 ment, the process is repeated. 



In the same way infection by way of the alimentary tract 



