NATURAL SCIENCE 



A Monthly Review of Scientific Progress 



No. 77— Vol. XIII— JUIA 1898 



Specific Characters in Bacteria 



In the April number of the Scottish Medical and Surgical Journal 

 Dt Alexander Johnson records two cases of puerperal fever success- 

 fully treated by the antistreptococcic serum. There are many 

 similar cases recorded, and there are also many in which serum 

 treatment has been unavailing. The matter is not merely one of 

 medical importance, but involves a problem of no small interest to 

 the biologist — the question, namely, of specificity amongst bacteria. 

 Even among the higher plants and animals this question is not 

 rarely a matter of dispute, although as a rule, morphological charac- 

 ters are alone at issue. It is not surprising therefore, that amongst 

 bacteria, — where morphology alone is of little value as a means of 

 specific distinction, though it is useful enough in differentiating 

 genera — the difficulties which arise should be even more acute. 

 In distinguishing between allied species, bacteriologists employ, 

 besides morphological characters, staining reactions, cultural charac- 

 ters, chemical and physiological properties, and powers of pathogenesis. 

 To these aids to diagnosis there has been added, in the last few 

 years, an altogether novel one — the capacity for specific immunisa- 

 tion, together with the remarkable power possessed by the serum of 

 immunised animals, in the case of certain bacteria, of agglutinating 

 the bacteria against which they have been immunised. Thus, to 

 take a concrete example, supposing that it be desired to distinguish 

 the bacillus of typhoid fever from one of its nearest allies, the 

 common colon bacillus, the bacteriologist can rely largely upon 

 morphological distinctions, and in particular upon the character and 

 number of the cilia demonstrable by the methods of Loffler, Pitfield, 

 or Van Ermengem. He can trust also to chemical tests — to the 

 powers possessed by the colon bacillus of coagulating milk in virtue 

 of its more active acid production, of its rich powers of gas forma - 

 tion, or of indol production — powers which the typhoid bacillus does 

 not possess. But he can now adopt a new method. He can 

 immunise an animal, by repeated injection of sub-fatal doses, against 

 the colon bacillus or the typhoid bacillus, and he can test the power 

 possessed by the serum of such immune animals of agglutinating the 

 bacillus which he wishes to test. Serum from an animal immunised 



