612 INFECTION AND IMMUNITY. 



atrium, and transmission probably is accomplished chief- 

 ly through the secretions of the respiratory passages. 

 In the udders the process may at first be one of miliary 

 tuberculosis, but a large amount of fibrous tissue forms 

 in time, many acini are transformed into retention cysts, 

 in which tubercle bacilli, free or intracellular, may be 

 present in large numbers. 



Aside from anatomic changes and clinical symptoms, 

 diagnosis depends on the tuberculin reaction, and, in 

 relation to the udder, the demonstration of bacilli in the 

 milk by staining methods or inoculation into guinea- 

 pigs. 



The tuberculin reaction in cattle is similar to that in 

 man and is subject to the same general limitations, but 

 is used extensively with the most satisfactory results. 

 The complete elimination of tuberculosis from herds of 

 cattle is possible, by using tuberculin as a diagnostic 

 test, the slaughtering of infected animals, and the dis- 

 infection of stalls. 



Tuberculosis among sheep and goats is rare. It occurs 

 occasionally in the horse, hog and dog, and with more 

 frequency in the cat. 



Avian A f rm of tuberculosis is very common in the chicken, 

 Tuberculosis, and attacks also the pheasant, dove and turkey. The 

 duck and goose are exempt from it. Although the or- 

 ganism resembles that of human tuberculosis in size, 

 staining properties and other general characteristics, 

 differentiation is accomplished by means of the follow- 

 ing points: 1. The avian bacillus shows a greater tend- 

 ency to pleomorphinism as shown by club-shaped forms, 

 unstained vacuoles, "spore-like" bodies, and branching 

 threads. 2. It has a greater affinity for aqueous anilin 

 dyes. 3. Growth takes place in artificial media more 

 rapidly and on solid surfaces is characterized by its 

 moist appearance and mucus-like consistence in contrast 

 to the dry, warty, brittle growth of the human bacillus. 

 4. The optimum temperature for growth (from 40 to 45 

 C.) is several degrees higher than that of the mamma- 

 lian organism. 5. Its pathogenicity for guinea-pigs is 

 less and for rabbits greater than that of the human and 

 bovine bacilli. Their difference in pathogenicity is 

 further shown by the difficulty which is met in trying to 

 infect fowls with the human bacillus. By varying the 

 conditions of cultivation and by animal passage the two 

 may be made to resemble each other very closely, al- 

 though the permanent transformation of the human into 

 the avian, or vice versa, has not been accomplished. 



