542 IMMUNOLOGY 



conclusions which he holds as a result of an extensive study of 

 spontaneous bovine tuberculosis and paratuberculosis may be 

 summarized as follows: 



Summary of Theobald Smith 's Studies of Spontaneous Bovine 

 Tuberculosis. — 1. Whereas the concept of phagocytosis has been 

 regarded as a one-sided affair, in reality one can only postulate that 

 certain bacteria and cell types possess an affinity for each other. 

 The results of such mutual attraction may vary from death of 

 the host to partial or complete suppression of the parasite. In 

 tuberculosis, paratuberculosis, leprosy, glanders, as well as in 

 induced Brucella infections in guinea pigs, the bacteria associated 

 themselves with cells of the connective and adenoid tissue. Their 

 association leads to the development of the epithelioid type of 

 cell. In typhoid and paratyphoid infections the bacteria liave 

 an affinity for endothelial leucocytes, while in diseases due to 

 llickettsia and in mouse septicemia the organisms exhibit a marked 

 affinity for vascular endothelium. 



2. In his opinion both allergy and immunity in tuberculosis 

 result from the ''discharge of diffusible products of the living 

 bacilli and the continuous impact of these substances in minute 

 doses upon the forerunners of tlie epithelioid cells throughout tlie 

 system. ' ' 



3. He observed that in spontaneous bovine tuberculosis the 

 secondary foci exhibit definite evidence of having developed un- 

 der the influence of an acquired immunity. In contrast with the 

 primary lesions they are smaller, show a lessened tendency to 

 necrosis, and contain giant cells. 



4. The primary focus of epithelioid cells observed in spontane- 

 ously acquired bovine tuberculosis is not invaded by neutrophiles 

 as in experimentally induced bovine tuberculosis. The neutro- 

 philes do not seem to be involved in the initial stages of spon- 

 taneous tuberculosis. 



5. He attributes a dual role to the focal lesions in tuberculosis. 

 They are places where the bacteria multiply and places where 

 the micro-organisms are being opposed by the host. The focus 

 represents a compromise between the host and parasite. 



6. In his opinion it is impossible to visualize all of the factors 

 involved in the inner workings of the tuberculous focus because 

 they are in a state of change. In the primary lesion of spon- 



