INFECTIOUS DISEASES OF CATTLE. 443 



been passed through various species of animals, by making the cul- 

 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. But far from decreasing in virulence, as might be expected 

 from its morphological appearance, this bacillus had so increased in 

 its pathogenic activity that it now produced generalized tuberculosis 

 in a cow. This cow was inoculated subcutaneously in front of each 

 shoulder with 2 c. c. 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 inoculation and adja- 

 cent glands greatly swollen. The autopsy revealed generalized tuber- 

 culosis, 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 trans- 

 formed 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 suc- 

 cumbed in a shorter time than the first of the series. 



These 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 piscine types of tubercle bacilli several years ago, 

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

 types. 



It must be plain to all, from these recent developments, that too 

 much has been made of the slight diiferences in cultural character- 

 istics, in morphology, and in virulence which have been observed in 

 some cases in comi^aring the human and the bovine bacilli. The 

 observations were interesting, and it was important that they should 

 be followed up until their significance was made entirely clear; but 

 it was an almost unpardonable error, from a sanitary point of view, 

 to promulgate sweeping generalizations calculated to arrest and 

 abolish important measures for preventing human tuberculosis before 

 the soundness of these generalizations had been established by a 

 thorough course of experimentation. 



When Koch said in the British Congress on Tuberculosis that he 

 should estimate the extent of infection by the milk and flesh of tuber- 

 culous cattle and the butter made of their milk as hardly greater than 

 that of hereditary transmissioii, and that he therefore did not deem 



