AVIAN TUBERCULOSIS 343 



more healthy outdoor life with exercise which this animal generally 

 leads makes it much less susceptible to the natural infection than 

 man, cattle, or swine. When tuberculosis is encountered in the horse 

 it is generally found in young animals in which the mesenteric and 

 other abdominal glands are the favorite seat of infection. These 

 glands are found enlarged and form agglomerated nodular tumor 

 masses; the mesentery and omentum are thickened and the intestinal 

 mucous membrane often shows tuberqular ulcers. The tubercular 

 masses may surround large veins, compress and discharge into them 

 tubercular material, bringing about a general acute miliary tuber- 

 culosis. In abdominal tuberculosis in the horse the spleen is frequently 

 found involved, the liver rarely. The former may assume a large size 

 and may weigh twenty to twenty-five pounds. Primary pulmonary 

 tuberculosis in the horse generally is of the miliary type; the large 

 tubercular nodules and masses seen in cattle rarely occur; the peri- 

 bronchial lymph nodes are found enlarged and studded with yellowish 

 nodules, while the respiratory mucosa is sometimes ulcerated. When 

 the serous membranes, the pleura, and the peritoneum are the seat of 

 tubercular lesions in the horse, they present a picture similar to pearl 

 disease in cattle. 



Tuberculosis in Food-producing Animals in the United States. Melvin, 

 in a paper on the Economic Importance of Tuberculosis of Food- 

 producing Animals, read before the Sixth International Congress on 

 Tuberculosis, held in Washington in 1908, reported that the following 

 number of animals were found tubercular among a total of 53,973,337 

 head slaughtered in the United States, under federal inspection, during 

 the fiscal year 1907-08: 



Tubercular cattle 68,395 



Tubercular calves ' ; . . . . . . 524 



Tubercular hogs 719,300 



Tubercular sheep ., 40 



Tubercular goats .'...' ".'".. 1 



Loss for condemned cattle, $710,677; hogs, $1,401,723. The same 

 author estimates the loss due to tuberculosis among meat- and milk- 

 producing animals in the United States at $14,000,000 annually. 



Avian Tuberculosis. Robert Koch, in 1882, was of the opinion 

 that avian and mammalian tuberculosis were the same disease and 

 due to an identical microorganism. Later, however, he withdrew 

 from this belief, and the preponderance of evidence today is that these 

 two types of tuberculosis are not absolutely identical, but that they 

 are in some important respects dissimilar diseases, due to two different 

 varieties of the tubercle bacillus. Avian tuberculosis occurs among 

 chickens and pigeons, also occasionally among geese and ducks. 

 Natural infection occurs when healthy animals feed upon material 

 soiled with the discharges of tubercular birds or when they directly 

 eat some of the tubercular organs. Tuberculosis in birds most 

 commonly occurs in the abdominal organs and the intestines and 



