232 PATHOGENIC BACTERIA IN MILK 



those disease-producing bacteria that are common to all the 

 domesticated animals are also able to produce disease in man. 



We cannot pursue the subject further in this place, particularly 

 as the whole matter is sub judice until the report of the larger 

 experimental work of the Royal Commission is published. 



The provisional attitude we take up at the present is the same 

 as that which we have adopted throughout our work on the 

 bacteriology of milk, namely, that tuberculosis in all animals is 

 generically one and the same disease, but that it differs in various 

 ways in different animals, and according to the strain and virulence 

 of the infecting bacillus. That human tuberculosis can be trans- 

 mitted under certain circumstances to animals, we do not doubt. 

 There is also prima facie evidence to show that the reverse proposi- 

 tion is true, namely, that under certain conditions bovine tubercu- 

 losis is transmissible to man. We therefore look upon the two 

 diseases as different species or varieties of one and the same 

 generic disease, and intercommunicable. Whilst we hold this view 

 in respect to the communicability of tubercle, we do not for one 

 moment suppose that its transmission through milk is very 

 frequent or very wide spread. The great field of infection in 

 tuberculosis is from animal to animal and from man to man, and 

 cross-infection is probably less common than is generally supposed. 



The Biology of the Bacillus Tuberculosis 



The comparative biology of the Bacillus tuberculosis and its 

 allies becomes every year more complex. As early as 1884 

 Koch pointed out that it was not improbable that in time other 

 bacteria would be discovered possessing the same tinctorial pro- 

 perties as the tubercle bacillus. This was but the first step in 

 the study of its allies, which have now been found to be numerous. 

 Secondly, the tubercle bacillus itself has been proved to exist in a 

 variety of polymorphisms. In the third place, certain patho- 

 logical conditions have been found to simulate in a marked 

 degree the "tubercles" having their origin in the growth of the 

 specific tubercle bacillus. For some time these allied conditions 

 were known as " pseudo-tuberculosis." It is in the main these 



ments it was found that in the scale of comparative racial susceptibility the 

 herbivora (cattle, sheep, goats) proved highest, then swine, and after these 

 guinea-pigs and rabbits. Carnivorous animals were little affected. Bovine 

 tubercular matter was found to possess the greatest power of infection, then 

 came the sputum of tuberculous men, then the milk of tuberculous animals, 

 and lastly, tuberculous flesh. 



