TUBERCULOSIS. 435 



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 charactres, 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. 



These experiments and observations indicate that the tj^pes 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 differences in cultural character- 

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

 some cases in comparing the human and the bovine bacilli. The 

 observations were interesting, and it was important that they 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 transmission, and that he therefore did not deem 

 it advisable to take any measures against it, he went far beyond what 



