Human and Bovine Tuberculosis. 43 



in temperature of nutrient media, etc. may affect the bacillus of 

 anthrax and render it almost inert, and that it may take some 

 time and special conditions for the restoration of the original 

 virulence. It is recognised too that the resistance of individuals 

 of the same species may vary enormously even to the same 

 organism, and that this comes out most markedly in the case of an 

 organism of modified virulence. If this holds good in the case of 

 the anthrax bacillus, may it not be equally true in the case of the 

 bacillus tuberculosis ? 



Here we have to remember however that we have an organism 

 that grows comparatively slowly. In the first instance it sets up 

 localised lesions which in most cases at any rate are of slow 

 development. 



A slowly growing organism and one that causes such com- 

 paratively slowly developing lesions will in all probability undergo 

 comparatively slow and slight modifications when it is placed in 

 new environments and is subjected to new conditions. The direct 

 evidence on these points is at present very small in amount and 

 unsatisfactory in character. We have little evidence of a morpho- 

 logical character. Pathologists have had so much to undertake in 

 connection with the study of the bacillus in the tissues and in 

 ordinary "culture" conditions that they have had little time or 

 opportunity to devote to the changes in morphological and 

 biological characters of the tubercle bacillus outside these two 

 limited areas. 



The tuberculin reaction however has given us some evidence 

 that the differences insisted upon by Koch and his followers are 

 not specific, indeed are scarcely to be dignified by the term 

 varietal, but the large field of biological and morphological inves- 

 tigation that is just being broken, will I believe prove a most 

 fruitful field to men trained in these branches of study, and how 

 warmly their cooperation will be received it is scarcely necessary 

 for me to emphasise. 



As far as can be gathered from the information now at our 

 disposal, the character of the lesions set up by different varieties 

 of the tubercle bacillus, the specificity of the reactions obtained 

 with tuberculin derived from bacilli derived from human and 

 bovine sources, the evidence slight though it be of modification of 

 morphological and biological characters, and especially the more 

 marked evidence of gradation of virulence in the two types as 

 usually described, we are, I think, justified in assuming that some 

 time or other we should be able to find links connecting even the 

 distant extremes, in spite of the great difficulties encountered in 

 tracing these links, difficulties that arise out of the comparatively 

 slow growth of the tubercle bacillus both in culture and in the 

 tissues, and the correspondingly slow development of the tuber- 

 culosis induced by them. 



