SIGNIFICANCE OF ALLERGY 543 



taiieous ])oviiie tuberculosis the early development of central 

 necrosis masks the earliest phases. He assumes that the latter 

 consist of the multiplication of the bacteria, the swelling of the 

 cytoplasm of the local tissue cells, and then the development of 

 central necrosis. The diffusion outward of products of metab- 

 olism of the tubercle bacillus leads to the formation of the epi- 

 thelioid cell mantle and connective tissue capsule. 



7. He points out that immunity in tuberculosis tends toward a 

 diminishing susceptibility instead of an increased activity on the 

 part of the cells. This results finally in the feeblest reaction, the 

 formation of the giant cells. It is evident that this conclusion of 

 Theobald Smith's is in harmony with the view of Rich and others 

 that immunity and allergy are not necessarily identical. 



The Immunizing Value of Nonprogressive Primary Lesions. — 

 Lurie (1933), in his experimental studies of contact tuberculosis, 

 seems to have avoided many of the sources of error which have 

 just been discussed. In 1930 he reported that cattle immunized 

 with von Behring's bovovaccine were resistant for several months 

 to the artificial introduction of fatal doses of tubercle bacilli of 

 the bovine type. When, however, such immunized animals were 

 stabled for twelve or more months with tuberculous cattle that 

 were eliminating virulent tubercle bacilli, the immunized animals 

 acquired tuberculosis. Such conditions of exposure to infection 

 ai"e to a certain extent comparable to the environment of a child 

 in contact with tuberculous parents. Lurie also studied contact 

 tuberculosis in guinea pigs. It was evident from these studies 

 that the route of infection depended upon the relative intensity 

 of exposure by the respiratory or alimentary channel. He deter- 

 mined that the reason crowding is so conducive to the spread of 

 tuberculosis is the amount of virulent tubercle bacilli available 

 for contagion. 



In 1933 Lurie produced localized, nonprogressive infection in 

 rabbits by inoculating them with living tubercle bacilli of the 

 human type. When such rabbits were used as cage mates for 

 normal rabbits, the latter died with contact tuberculosis. In order 

 to ascertain the effect of such localized, nonprogressive tuberculosis 

 upon the resistance of rabbits to contact infection with 

 virulent bovine tubercle bacilli, Lurie exposed these infected 



