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NATURAL SCIENCE 
A Monthly Review of Scientific Progress 
No. 77—Vo.t. XITI—JULY 1898 
SPECIFIC CHARACTERS IN BACTERIA 
In the April number of the Scottish Medical and Surgical Journal 
Dr Alexander Johnson records two cases of puerperal fever success- 
fully treated by the antistreptococcus 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 
lmmunise 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 
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