INHIBITORY ACTION OF PARATYPHOID BACILLI ON 



THE FERMENTATION OF LACTOSE BY 



BACILLUS COLL I. 



By THEOBALD SMITH and DOROTHEA E. SMITH. 



(From the Department of Animal Pathology of The Rockefeller Institute for Medical 

 Research, Princeton, N. J.) 



(Received for publication, July 8, 1920.) 



In nature, organic matter is attacked by a large variety of bacteria 

 and in its disintegration a number of species may take part. A knowl- 

 edge of just how the species are associated in any given substrate or 

 in what order they succeed one another in the process of decomposi- 

 tion might be of great value to the biochemist in supplying a point 

 of approach hitherto neglected. There is evidence that there is some 

 order in the mode of attack and that this order is conditioned by the 

 nature of the medium and certain environmental factors, such as 

 temperature, reaction, and oxygen supply. In the following pages 

 one single detail of this general problem was examined under condi- 

 tions which excluded all but two bacteria, one following the other. 



If a fermentation tube containing fermented bouillon plus 1 per 

 cent lactose be inoculated with some member of the paratyphoid 

 group, the multipHcation causes a heavy clouding or even turbidity 

 in the open arm. 



The growth in the closed arm depends on the degree to which the 

 muscle sugar has been removed. If this is complete, no growth takes 

 place. The clouding of the branch is therefore proportional to the 

 amount of muscle sugar remaining. Titration shows little or no 

 change of reaction in the closed arm, beyond what is due to a move- 

 ment of fluid from open to closed arm. The fluid in the open arm 

 becomes neutral and finally alkaline to phenolphthalein, the degree 

 of alkalinity being a function of the multiplication which in turn is 

 a function of the alkali-tolerance of the particular strain used. If 

 after 4 to 6 days of incubation the same tube is reinoculated, this 

 time with a true colon bacillus known to ferment lactose, one of two 



things may happen : 



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