TUBERCULOSIS 273 



Infection. The organisms enter the body through either 

 the respiratory or the alimentary tract. The importance 

 of these portals of entrance varies in different animals. It 

 is probable that the bovine becomes easily infected in either 

 of these ways, while in the case of the hog the infection 

 under natural conditions is by way of the alimentary tract. 

 The guinea-pig, one of the most susceptible animals, ac- 

 quires the disease with ease by the inhalation of the bacilli, 

 while it is very resistant to infection through the alimentary 

 tract. 



Lesions. The lymph-glands, which are widely distrib- 

 ute! I in the body, are to be looked upon as filters, and tend 

 to remove any foreign solid particles, such as tubercle ba- 

 cilli, that have entered the lymph or blood circulation. The 

 bacilli are most likely to lodge in those glands that are in 

 close proximity to the point of invasion. Thus, the neck 

 glands are most frequently diseased in the hog, and the 

 glands near the lungs and intestines in the bovine. The 

 lungs, liver, and spleen are also frequently tubercular. 

 The organs mentioned are those to which the greatest at- 

 tention should be paid in making a post-mortem examina- 

 tion. Any organ may be tubercular, such as the heart, 

 brain, udder, and neighboring lymph-glands, the joints, 

 bones, and infrequently the lymph-glands located in the 

 muscles. 



The bacilli collect in some of these organs and grow 

 slowly. Their by-products exert a stimulus on the body 

 cells in the immediate vicinity, causing the formation of the 

 characteristic tubercles or nodules. The tubercle is most 

 evident when located on one of the smooth serous mem- 

 branes of the body, producing that type of disease known 

 as pearl disease or grapes. The cells at the center of the 

 tubercle are soon killed by the. poison elaborated by the 

 bacilli. As the area of the dead tissues continues to in- 



