664 ARTHUR ISAAC KENDALL 



tion of the limits surrounding the uses of vaccines for therapeutic pur- 

 poses, are also significant events of this decade. The preparation of 

 specific serums, begun in this period, represents as yet an immature phase 

 of bacteriotherapy, but it is a most promising field for further study. 



Progress up to the present time in medical bacteriology, therefore, has 

 been chiefly along diagnostic lines, both with reference to the isolation and 

 identification of the etiological agents of specific microbic diseases, and 

 with reference to the recognition of serological reactions in infected indi- 

 viduals. Indeed, with the exception of those few bacteria to whose soluble 

 toxins specific antitoxins have been prepared, the advances in the ameli- 

 orative and curative aspects of medical bacteriology have been disappoint- 

 ingly limited. Yet this is the most important field of all. 



It is quite apparent that a shifting of the point of attack must precede 

 further advances. Diagnostic, or morphologic, bacteriology must give 

 place to dynamic or chemical bacteriology. "It is what bacteria do rather 

 than what bacteria are that commands our attention, since our interest 

 centers in the host rather than the parasite," as Theobald Smith has so 

 aptly said. The application of biochemical methods to the elucidation of 

 conditions which surround the preparation of soluble toxins, and which, 

 therefore, permit of the generation of potent antitoxins is a striking 

 example of the correctness of this dynamic principle: Those same phe- 

 nomena which influence the formation of toxin in cultures of diphtheria 

 bacilli play a very important part in determining the nature of the 

 significant products formed by other pathogenic bacteria. 



It is not without significance that those very procedures which Escher- 

 ich and the long list of bacteriologists following him have found useful, 

 and even essential for the identification of microbes have their origin and 

 explanation in these bacteriochemical studies of the mode of action of 

 bacteria. In this regard, bacteriology merges imperceptibly into the fields 

 of protein and carbohydrate chemistry. 



Also, the explanation for the striking alternations of bacterial types 

 in the alimentary canal in response to dietary stimuli, and for the con- 

 ditions which surround the production of endogenous, physiologically ac- 

 tive bacterial putrefaction products, depends upon the same biochemical 

 principle of bacterial metabolism. The amelioration, or even the rectifica- 

 tion, of exogenous and endogenous disturbances or infections of microbic 

 causation in the alimentary canal can be accomplished through the simple 

 and direct application of the same metabolic principle. A new science, that 

 of baeteriochemistry, is gradually forging into prominence. A new field 

 in medical bacteriology is developing. In this new field, certain funda- 

 mental principles underlying the metabolism of bacteria, are being ex- 

 ploited in the direct interest of the host. The nature of these principles, 

 their limitations, their relation to bacteria, and to bacterial infections of 

 man, are discussed in the following pages. 



