148 DISEASES OF SWINE 



the pig may have choking spells. Abnormal lung 

 sounds are heard on auscultation. 



In tuberculosis of the brain, nervous symptoms, 

 such as turning round and round, convulsions, 

 spasms of muscles and paralysis, occur. The 

 head may be held obliquely, the snout drawn to 

 one side, and the ears allowed to droop. Certain 

 parts of the body or groups of muscles are usually 

 involved. 



The course of generalized tub.erculo3is is short 

 in young pigs, but may last for months in older 

 ones. When the disease is localized and the tis- 

 sue changes in the vital organs are not advanced 

 or extensive enough to seriously interfere with 

 the body functions, the true nature of the disease 

 is not recognized until after the animal is slaugh- 

 tered. 



Lesions. — The changes in the tissues following 

 the invasion of the bacillis tuberculosis are the 

 formation of nodules or tubercules, gray or yel- 

 lowish white in color, or translucent in character. 

 In some cases the nodules are distinct and easily 

 recognized, but in advanced cases they often come 

 together and form a mass of tubercular tissue. 



In the beginning the tubercle consists of a few 

 cells surrounding the invading germs. These are 

 soon enclosed in a zone of epitheloid and giant 

 cells, which in turn become surrounded by a 

 layer of lymphoid cells. The central portion of 

 the tubercle soon dies and breaks down, and as 

 the nodule enlarges, the necrotic portion gradually 



