436 DISEASES OF CATTLE. 



tures upon dog serum after the method described by Theobald Smith. 

 Some important results have been obtained. One culture of human 

 bacilli which had morphological and cultural peculiarities similar to 

 those of the bovine bacillus, and which produced only local lesions in 

 cattle, was passed through a series of five cats. It was then found to 

 be completely changed in its morphological characters, the rods being 

 elongated, slender, more or less beaded, and entirely of the human 

 type. Far from decreasing in virulence, however, as might be ex- 

 pected from its morphological appearance, this bacillus had so in- 

 creased in its pathogenic activity that it produced generalized tuber- 

 culosis in a cow. This cow was inoculated subcutaneously in front 

 of each shoulder with 2 cubic centimeters of a salt-solution emulsion 

 of the tuberculous omentum of the last cat of the series. The cow 

 rapidly lost flesh, had a temperature of 104° F., with the point of in- 

 oculation and adjacent glands greatly swollen. The autopsy re- 

 vealed generalized tuberculosis, involving the lungs, mediastinal 

 glands, spleen, liver, and kidneys. Tubercle bacilli of the bovine 

 type obtained from the mesenteric glands of a sheep, hog, and cow 

 were similarly transformed in their morphological appearance after 

 being passed through a series of cats and recovered on dog serum. 

 These bacilli also increased in virulence, as the last cat in the series 

 invariably succumbed in a shorter time than the first of the series. 



Tliese experiments and observations indicate that the types of 

 tubercle bacilli are very inconstant, and that under suitable condi- 

 tions they readily change both in morphology and in virulence. A 

 similar conclusion was reached by other investigators in working 

 with the avian and porcine types of tubercle bacilli several years ago, 

 and was reasonably to have been expected with the human and bovine 

 types. 



Later investigations made by Park and Krumweide, of the Research 

 Laboratory of New York City, Novick, Richard M. Smith, Ravenel, 

 Rosenau, Chung Yik Wang, and others tend to show the incidence of 

 bovine infection in the human family. Chung Yik Wang stated 

 in 1917 that studies of 281 cases of various clinical forms of tuber- 

 culosis in Edinburgh, Scotland, resulted in the isolation of the bovine 

 tubercle bacilli in 78.4 per cent of cases under the age of 5 years, in 

 70.3 per cent between the ages of 5 and 16, and in 7.8 per cent over the 

 age of 16. This investigator states that from the prophylactic point 

 of view any measure resorted to in combating the disease should be 

 directed not only against the human spread of infection, but also, 

 more particularly in children's cases, against the bovine source of 

 infection. 



