TUBERCULOSIS. 
325 
stomach and intestines. In tuberculosis of the kidneys or geni¬ 
tal glands the process may extend to the genito-nrinary mucous 
membrane. 
3. By Means of Circulation. —The bacilli may be dissemi¬ 
nated through the whole system when the destruction of a tu¬ 
berculous centre leads to perforation of a vein, or when the 
process directly invades the vascular walls (W. L. Z.) Another 
means by which the blood becomes contaminated with the 
tuberculous germs is by inoculation of the subcutaneous tissue. 
This is mostly the experimental way, and will be treated more 
fully under the head of tuberculin. 
In speaking more particularly of the predisposing causes of 
tuberculosis I will first consider 
Heredity. —Among the wild herds of the plains, tuberculo¬ 
sis is practically unknown, while among the cows of closely- 
confined dairy herds it is quite common. There is no proof of 
the direct inheritance of the disease, other than the transmission 
of weakened constitutions and lowered vitality : in other words, 
the transmission of hereditary susceptibility. 
In-and-in Breeding has the debilitating effect that is so con¬ 
genial to the ever-invading germ. This is readily demonstrated 
by an examination of the herds of cattle most susceptible to the 
disease, and it is found that this is the in-bred variety. On the 
contrary, the grade stock, or cross between some thoroughbred 
and common stock, is less susceptible. 
Lack of Ventilation. —Unsanitary conditions, as a matter of 
fact, are conducive to the spread and development of the disease. 
Close stabling, insufficient amount of air and sunlight, damp, 
underground stables are all a great source of danger, and I 
believe this to be one reason why our Western herds are less 
contaminated than those of the East. 
Breeding Too Young. —Over-stimulation for excessive milk- 
production, lack of exercise, with many other unnatural condi¬ 
tions which stock undergo, lead indirectly to the contraction of 
the disease. It is generally conceded that all animals are, at 
some time in their life, exposed to the germ and a large per- 
