344 TUBERCULOSIS AS A TYPE OF BACTERIAL DISEASE 



direct experiments on human subjects we infer that man also can 

 acquire tuberculosis by feeding upon materials derived from tuber- 

 culous food-animals." * 



Viewing all the facts, there can be little doubt but that this con- 

 clusion is the right one from the point of view of the public health. 

 Various circumstances have in all probability contributed to render 

 unsuccessful or irregular in result the numerous feeding experiments 

 which have been made. The tissues of animals differ greatly in 

 susceptibility to tuberculosis; the infective material is exposed to 

 the digestive juices which are, in measure, germicidal, and yet not 

 equally so ; the virulence of the infective material itself varies 

 enormously, as does the virulence between different generations or 

 races of tubercle bacilli. Hence it comes about that one animal 

 may eat with its food a certain amount of tuberculous material, and 

 yet not develop tuberculosis, whilst another animal of the same 

 species might quickly develop the disease, which would in all 

 probability show itself at the animal's weakest point, and not 

 always necessarily in the intestine. Further, there is another point 

 which should not be overlooked, namely, the subsequent treatment 

 of the inoculated animal. Whilst it is essential to prove that the 

 animal to be inoculated is free from tuberculosis, it should be 

 remembered that in taking very healthy animals for experiment, 

 and in subsequently treating them in what may be termed an 

 "ideal" fashion, some of the very conditions essential to the pro- 

 duction of the disease in ordinary life are removed. As in men, so 

 in cattle and other animals, it may be presumed that abundance of 

 good food and fresh air, and, in general, an ideal environment, tend 

 to counteract the effect of the inoculated or communicated virus. 

 Thus such experiments as those stated above may not always fairly 

 represent the modes of transmission of the disease as they occur 

 in ordinary life. It is not the "very healthy" animal of a herd, 

 well housed and fed, which contracts tuberculosis. 



As a result of the wide differences of opinion revealed by the 

 pronouncement of Koch's views, special Commissions of Inquiry were 

 instituted in Germany, Great Britain, and other countries, in addition 

 to the individual research work to which reference has been made. 

 As this book has been passing through the press, reports of these 

 inquiries have been made by the German Imperial Health Office and 

 the Royal Commission on Tuberculosis, appointed in 1901 by the 

 British Government. The conclusions are briefly as follows : 



Kossel, Weber, and Heuss, who carried out a comparative research 



upon tubercle bacilli of different origins, made a number of experiments 



on calves by injecting some forty different strains of human bacilli 



and fifteen strains from bovine, fowl, and swine sources. They con- 



* Report of Royal Commission, 1895, part i., p. 20, par. 77. 



