112 BULI,ETIN 65. 



While none of such accessory causes can generate tuberculosis 

 in the absence of the bacillus, yet when that diseased seed is 

 present, these conditions often serve to swa}'^ the balance toward 

 its advancement and diffusion, or its restriction and suppression. 

 A suitable soil and favorable climate is no less essential for the 

 vigorous growth of the microscopic vegetable microbe, than for 

 the Florida moss or the palm. 



Among the most efficient accessory causes may be named : 



a. Hereditary Predisposition. 



Consumption runs in families and it has long been supposed 

 that this was essentially a family — that is, a hereditary disease. 

 But as a matter of fact it is extremely rare to find the ojBFspring 

 tuberculous at birth or before. In many thousands of pregnant 

 tuberculous cows killed in the slaughter- houses of Europe not 

 more than ten tuberculous calves have been found. To the same 

 eflFect is the fact that in calves under a year old, born of cows, six 

 per cent, and upwards of which prove tuberculous, the ratio of 

 tuberculosis is often below one per thousand. In Saxony with 

 the ratio of tuberculous cattle 16.5 per cent, that of tuberculous 

 calves was only 2 per 1000. At I^yons out of 400,000 calves 

 slaughtered only 5 were found tuberculosis and at Munich out 

 of 400,000 but 2 tuberculous. Again in such calves the tubercle 

 is found in a very large proportion 'of cases in the bowels and 

 adjacent glands suggesting infection after birth through the milk, 

 rather than in the liver and lungs which would have been its 

 natural seat if conve5'ed before birth through the blood. Not a 

 few of the obstinate and fatal bowel diseases of sucking children 

 and calves are in reality tuberculosis of the bowels induced by the 

 infected milk. 



What runs in a family then is rarely hereditary disease : — 

 it is in the great majority of cases only a hereditary suscep- 

 tibility to the disease, tuberculosis. But it is none the less a fear- 

 ful legacy, being often so potent that the disease attacks certain 

 families as a matter of course, while other families can count on 

 a practical immunit}'. In the human family this is notorious. In 

 cattle it is no less remarkable. In the Burden herd of Jerseys in 

 1877, I made examinations, and condemned eleven animals, veri- 

 fying my diagnoses b}^ examinations after death, and found to my 



