THE COURSE OF INFECTIOUS DISEASE 



presumed to have a similar basic pathology : the lodgment of 

 a source of specific antigenic determinants and the accumula- 

 tion around the region of mesenchymal cells of the specifically 

 related clones. 



The real problem is the source of the antigenic deter- 

 minants. If we accept the evidence that tubercle bacilli are 

 not directly involved but are strongly suspected of having 

 some indirect role to play, the two possibilities may be 

 considered. 



(i) The tubercle bacillus is undergoing multiplication in 

 some form other than that of a cultivatable acid-fast bacillus. 

 In view of modern work on protoplasts and L forms, it is by 

 no means inconceivable that a form derived from the 

 tubercle bacillus, but lacking power to produce the charac- 

 teristic cell wall, might find an opportunity to persist as an 

 intracellular parasite of mesenchymal cells and still produce 

 some of the antigenic determinants that make it different 

 from any body component. The necessary assumptions are 

 {a) that the protoplast form is a permanent mutant not 

 cultivatable and only very rarely subject to reversion to the 

 acid-fast bacillary form, {b) that infected cells can on occa- 

 sion pass to various parts of the body and there initiate foci 

 by the combined action of the intracellular parasite and the 

 mesenchymal response to the foreign determinants, [c) that 

 in most cases the infected cells are gradually eliminated. 

 A corollary to such an hypothesis would be that in the 

 usual development of the tuberculous granuloma, the epithe- 

 lioid cells would probably contain the hypothetical proto- 

 plast form of the bacillus. 



This suggests an interesting experimental approach which 

 I believe has not so far been reported, namely that an 

 extract of tuberculous tissue composed mainly of uncaseated 

 epithelioid cells should function as a Kveim reagent. 



Recent reports by Scadding (1956) offer rather strong 

 support for this view but only if it is combined with the 

 recognition of a host difference in reactivity to the tubercle 



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