COMMISSION ON TUBERCULOSIS 319 



by bacilli of the human type, and, therefore, is presumably 

 due to inhalation of human bacilli. 



McFadyean, 1 also, from a critical survey of the experi- 

 mental evidence, concludes that (1) inhalation of tubercle 

 bacilli suspended in the air is a very certain method of 

 infecting susceptible animals ; (2) experimental infection 

 by the digestive tract is comparatively difficult to realise ; 

 (3) inhalation is probably the commonest natural method 

 of infection, both in man and in animals ; (4) infection 

 by the digestive tract can be inferred only when the 

 lesions are confined to the abdomen. He finally states 

 that " the whole of the experimental evidence on which 

 the theory of the intestinal origin of pulmonary tuber- 

 culosis in man was built up has been swept away." 



While the death-rate per 1000 living from all forms of 

 tuberculosis is about 1-64, that from phthisis is 1-14, so 

 that the greater part of the mortality from tuberculosis 

 must be ascribed to infection from human sources. There 

 still remains the residuum of glandular, abdominal, bone 

 and joint tuberculosis which is ascribed to infection with 

 the bovine bacillus. The experiments of the Royal 

 Commission on Tuberculosis favour this view, but an 

 alternative explanation is possible. Thus Spengler, Klem- 

 perer, and Baumgarten from direct experiments on man 

 assert that the bovine bacillus is not pathogenic to man, 

 and Spengler distinguishes two types of human tubercle 

 bacilli, (a) the " humanus brevis," the ordinary human 

 type, and (b) the " humanus longus " type. The latter 

 is very like the bovine bacillus in pathogenic action, but 

 after carefully weighing all the facts, Spengler considers 

 the true " bovinus " and the " humanus longus " types are 

 not identical. It may be then that the bacillus found in 

 certain human lesions and considered to be the bovine 

 variety is really this humanus longus variety. Even 



1 Jaurn. Roy. Inst. Public Health, vol. xviii, 1910, p. 705. 



