No. 7. DEPARTMENT OF AGRICULTURE. 695 



are some observations that indicate, that tubercle bacilli may be 

 carried much longer distances before they occasion visible disease. 



The disease after gaining a foot-hold in the body and after one or 

 more.tubercles are formed, the bacteria may invade other regions by 

 passing through tissue, by being distributed mechanically in cavities 

 or in canals or by being transported in currents of lymph or in the 

 blood. Progression of tuberculosis by continuity of structure is not 

 rare and explains the invasion of the pleura from the lung, or of the 

 diaphragm, and subsequently the pleura, when the peritoneum cover- 

 ing the abdominal side of the diaphragm is the seat of tubercles. 

 Infection ma}" be carried from one part of the lungs to another by 

 tuberculous material that is distributed through the bronchial tubes. 

 If tuberculous material is discharged into the pleural or peritoneal 

 cavity, it is scattered by the movements of the animal and of the 

 organs within these cavities, so widespread infection of the serious 

 membranes lining them may result. 



■^Vhere tuberculosis exists in an organ, it is customary to find the 

 lymphatic glands of that organ involved in a tuberculous process. 

 The bronchial and mediastinal lymphatic glands are usually tuber- 

 cular when the lungs are. Tuberculosis of the portal lymphatic 

 glands follows tuberculosis of the liver and similarly, we find infec- 

 tion of the mesenteric lymphatic glands and of the supra-mammary 

 lymphatic glands in tuberculosis of the intestines and of the udder 

 respectively. The most widespread infection occurs when tubercle 

 bacilli enters the circulation. This accident results from the per- 

 foration of a blood vessel wall and the subsequent discharge into the 

 blood current of the contents of a tubercle or tubercular abcess. 

 There is no part of the body that is exempt from the ravages of 

 tuberculosis. Some parts, however, are more predisposed to the at- 

 tack of the germ than others, some tissues are better adapted for 

 their growth than others and, therefore, the disease is more common 

 in some organs than in others. 



Where the germs are carried in the circulation and the form known 

 as acute military tuberculosis develops, the lesions are distributed 

 widely. This form of tuberculosis usually kills quickly and upon 

 post-mortem examination it is found that while the lesions are 

 numerous and widespread, they are often of the young gray form and 

 have not consolidated into the large 3'ellow cheesy masses. 



In discussing the symptoms of tuberculosis it seems best to di- 

 vide the disease generally into two classes: 1. The chronic form, 

 which is usual, and 2, the acute military form^ which is not so com- 

 mon. 



The symptoms of chronic tuberculosis depend upon the location 

 of the lesions and their extent. When the lesions are situated deeply 

 are are not of great extent, they may occasion no visible symptoms 

 of disease. In such conditions the infected animal may present the 

 picture of health and show no disturbance of function. Indeed in 

 some animals in which the lesions are both extensive and widely dis- 

 tributed and which have never presented noticeable signs of dis- 

 sease and are killed in prime condition for beef, the owner is aston- 

 ished to learn that his supjiosed healthy animal contains large 

 masses of tubercular tissue. Since the lesions of tuberculosis vary 

 so much in different cases, and it is not possible to give a description 

 of what can be designa.ted the characterigtic or even the usual symp- 



