400 
G. A. JOHNSON. 
the indirect or predisposing causes are many, among which 
may be mentioned the surroundings, such as poorly ventilated, 
poorly drained stables, confining too many animals in a limited 
space, in-and-in breeding, the over-production of milk, and in 
fact any condition that tends to vitiate the germicidal property 
of the blood. 
The principal modes of infection are, inhalation of the 
germs suspended in the air, and alimentation of substances con¬ 
taminated with the germs, as the flesh and milk of tuberculous 
animals, especially the latter. 
PATHOLOGY. 
Whenever a sufficient quantity of live tubercular bacilli 
find a lodgment in any tissue, they soon begin to multiply. 
Their presence and activity act as an irritating foreign body, 
which nature endeavors to remove or limit through the process 
known as inflammation ; this results in the formation of small 
granular bodies, known as tubercles; these coalesce and form 
masses varying in size from that of an ordinary pea to a mass 
two or three inches in diameter ; degenerative changes within 
the tubercle take place early, so that the older tubercle is com¬ 
posed largely of a disintegrated mass that contains more or less 
lime salts. 
In the ox, the tendency is to the formation of a strong, thick, 
limiting membrane, which tends to prevent the formation and 
escape of liquid pus. 
The germs may find lodgment and produce morbid lesions in 
any tissues of the body, but the lungs and the lymphatic sys¬ 
tem are the most common seats of the disease, while the mus¬ 
cular and adipose tissues are rarely affected. 
SYMPTOMS. 
The symptoms must of necessity vary according to the seat 
of the affection. Owing to the slow and insidious character of 
the disease, the absence of fever, the inability of the ox to make 
known any minor aches and pains that it may suffer, and the 
slight interference with the normal functions of the various 
organs of the body, it is almost an impossibility to physically 
