Pathogenicity. 509 



chances of infection. Inhalation throngh the mouth is more 

 effective than inhalation through the nostrils. The inhalation 

 of heavily infected air usually results in miliary tuberculosis 

 of the kings, while slightly infected air may produce only 

 isolated tuberculous foci which develop into cheesy pneumonia 

 processes or cavities (Cornet & Mayer). 



Infection also follows the injection of tuberculous material 

 into the vagina or its direct application to the mucous mem- 

 brane (Cornil & Dobroklonsky). Occasionally the first symp- 

 tom of infection is a swelling of the inguinal glands without local 

 changes. Finally direct application of virulent cultures to the 

 teats of the udder is followed by a progressive inflammation 

 of the milk ducts (Nocard, Nattan-Larrier). 



Variations in the Pathogenic Effect of Tubercle Bacilli of Dif- 

 ferent Origin. The results of experimental infection vary considerably 

 according to the origin of the tubercle baciUi or of the material con- 

 taining them, as well as according to the age and the species of the 

 experimental animals. With rare exceptions the bacilli of the bovine 

 tvpe possess a higher degree of virulence for mammals, including the 

 ape, than the bacilli of the human type. It seems immaterial, also, 

 whether the particular type of bacillus in question originates from one 

 species of animal or from another. The differences in the patbogemc 

 action are observed even in the guinea pig which is unusually suscep- 

 tible. These animals succumb much more rapidly to infection M'lth the 

 bovine tvpe than to infection with the human type (Smith, Gratia). 

 The difference in the results of these two types is much more marked, 

 however, in rabbits and in cattle. 



The difference between the two types in their effect on rabbits was 

 recognized bv Villemin and later by Orth, Baumgarten, Vagedes, Smith, 

 Dorset Kossel, Heuss, Rabinowitsch and others. According to Weber 

 this may be summed up as follows : The bacilli of the bovine type when 

 injected intravenouslv in 0.001 g. doses wall kill rabbits in three w^eeks, 

 while the bacilli of the human type similarly administered produce at 

 first no conspicuous morbid symptoms, but in the course of several 

 months symptoms of chronic tuberculosis develop which affects chiefly 

 the articulations, the kidneys, the lungs and the testes. The bacilli of 

 the bovine type injected subcutaneously into the abdominal wall m 

 0.01 g. doses^ (not under the fascia into the muscles) produce a lung 

 tuberculosis which terminates in death in a short time. The bacilli of 

 the human tvpe will not produce these results. 



The effect of the two types of tubercle bacilli on cattle has, in 

 recent times, been the object of almost innumerable experiments. These 

 experiments as far as they have been limited to the use of pure cultures 

 have given comparatively uniform results, viz., that the bacilli of 

 the human type possess either a slight, or no pathogenic action what- 

 ever for cattle and that the bovine type, on the other hand, possess very 

 marked pathogenic properties with regard to cattle. Thus the subcutane- 

 ous injection of bovine bacilli, injection into the circulation or into the 

 peritoneal cavity usually produces severe progressive tuberculosis. Young 

 animals occasionally become affected in the same manner by the ingestion 

 of infected material. On the other hand inoculation of cultures of the 

 human type produce a local affection only or remain without any 

 pathogenic effect. This is particularly true if the dose of pure culture 



