PATHOGENIC MICROBES— INFECTION 115 



from the B. coli which is so abundant in the normal intestine. 

 Two principal types can be distinguished, A and B : the latter 

 is nearer to the B. coli, the former to the B. typhosus. They 

 are called para-typhoid or para-coli bacilli, but do not on that 

 account call in question the specificity of the Typhoid bacillus ; 

 the latter rather appears as a chosen specimen out of a 

 numerous family containing other well-defined pathogenic 

 bacteria, among which are not only these para-A and B, but 

 various bacilli producing meat-poisonings, diarrhoea among 

 animals, and the pneumo-enteritis of pigs. This family is 

 even the one in which the biological reactions have been 

 found most suitable for establishing fairly definite degrees of 

 relationship. We class them by their relations to the human 

 species, putting at the head of the column the typhoid 

 bacillus. It is evident that if we were calves or pigs our point 

 of view might be somewhat modified. 



One of the properties characterising the tubercle bacillus of 

 Koch is its acid-fastness (it takes on stains with difficulty, but 

 once stained by the suitable colour, it resists the decolorising 

 action of acids). There exist numerous acid-fast bacilli and 

 even numerous bacilli capable of producing tubercles in the 

 tissues. Between the human and bovine bacilli and the 

 bacilli found in grass, in manure, and even in smegma, there is 

 a long series of intermediate types. Are we to believe that 

 among the acid-fast and para-tubercle bacilli the ancestor of 

 the tubercle bacillus of men and the ox is to be found ? It is 

 rather a philosophical question and escapes experimental 

 examination. But the general truth of the Darwinian ideas 

 compels us to this belief. According as one is physician or 

 veterinary surgeon, according as one is engaged in diagnosis or 

 in treatment, according as one is accustomed to think as a 

 naturalist and to class all living beings in groups, so one tends 

 to insist on differences on the one hand, on resemblances on 

 the other. The production of tuberculin and the re-inoculation 

 of tuberculous lesions in series in a given species are methods 

 of differentiation which do not invalidate the existence of a 

 great natural family. 



