VIRULENCE OF TUBERCULAR MILK 243 



Martin reported, as a result of his experiments, that " the milk 

 of cows with tuberculosis of the udder possesses a virulence which 

 can only be described as extraordinary." ^ All the animals he 

 inoculated with milk from tuberculous cows showed tuberculosis 

 in its most rapid form, such as is seen after inoculation with a 

 recent tubercular lesion. In experiments for the same Commission, 

 Woodhead records similar conclusions. " Raw milk from tubercular 

 udders," he says, " is in all cases possessed of the power of setting 

 up tubercular infection, even when mixed with considerable quan- 

 tities of sound milk, whilst in some cases it possesses this power 

 in a most remarkable degree." - 



Nor is the virulence wholly a question of species. When steril- 

 ised milk is inoculated with tubercle bacilli derived from a 

 culture on serum, or from the tubercular deposit of the organs 

 of a guinea-pig, it shows after fourteen or twenty days at 37° C. 

 a growth of tubercle bacilli in the deeper layers, the milk 

 remaining unchanged. Such growth consists of typical clumps of 

 bacilli. After six weeks the number of such clumps is greatly 

 increased. But more than this, for it is found that the virulence 

 of such milk is more exalted than the virulence of the original 

 culture (Klein). Old non-pathogenic cultures of tubercle bacillus 

 or glycerine-agar may thus be changed into virulent agents with 

 marked pathogenic action. The same increase in virulence follows 

 sub-culturing from milk to milk. Similar experiments with cheese 

 or cream gave negative results.^ It is not suggested, it need 

 scarcely be added, that this increase of virulence in sterilised milk 

 cultivation is of a high degree ; indeed, there is evidence to the 

 contrary ; nor is it to be supposed that an exactly similar condition 

 appertains in the case of ordinary milk which becomes infected 

 with tubercle bacillus. The two cases are not similar, for in the 

 latter instance there is, as we have seen, the enormous increase of 

 other milk bacteria, whose rapid growth might exert an inimical 

 effect upon a small infection with the tubercle bacillus. 



On the other hand it has been shown that dilution of tuber- 

 culous milk with water or sound milk lessens the degree of its 

 virulence (Bollinger and others), and there may be other condi- 

 tions in milk, at present unknown, which diminish the virulence 



^ Royal Commission on Tuberculosis Report, 1896, Appendix, Inquiry ii., par. 

 148. 



^ Ibid., Inquiry iii., par. 120. 



' Twenty -Ninth Annual Report of the Local Government Board. Medical 

 Officer's Supplement, 1899-1900, pp. 577-585. 



