180 ^^^6 Philippine Journal of Science ms 



peptone-waters a slightly greater amount of acid sometimes 

 developed than in the corresponding bouillons. 



The degrees of acidity required to show change in litmus serum- 

 waters may be demonstrated by adding very dilute normal acids 

 to measured quantities of the medium. Acid up to or slightly 

 above the equivalent of 0.1 per cent usually causes no reaction, 

 an inertia due possibly to the "buffer" effect of serum, which 

 Levy and Rowntree(27) found to be from 0.1 to sometimes 0.3 

 per cent for fresh serum, which amount of acid could be added 

 without raising the hydrogen ion concentration; This margin 

 is too slight to be responsible for the occasional apparent fer- 

 mentation inactivities in serum media. Faint change usually 

 occurs with between 0.1 and 0.2 per cent acidification, while 

 coagulation is complete with less than 1 per cent, the reactions 

 being identical with hydrochloric and lactic acids. The different 

 changes are brought about regularly in different lots of the 

 medium by fairly definite amounts of acid, which makes the 

 observation of such reactions of approximate quantitative value 

 up to the point of coagulation of the serum. 



The unmodified litmus serum- waters of Hiss, although valuable 

 in the identification of intestinal and of other organisms, 

 have repeatedly proved unreliable and misleading with B. pestis. 

 Similar experiences have been had by other observers with 

 bacteria of low fermentation activity, as for instance certain 

 streptococci. That the reactions obtained do not result from a 

 directly inhibitory effect of the serum is indicated by the fact 

 that no suggestion of inhibition was shown in bouillons to which 

 serum had been added. Further, the addition of peptone some- 

 times increases the reaction, although this acceleration is not 

 constant enough with the different sugars to make such a 

 medium of general value in a study of bacterial fermentation. 



CONCLUSIONS 



Comparison has failed to demonstrate any distinct difference, 

 qualitative or quantitative, between the fermentation activities 

 of Oriental (Philippine) and certain American strains of B. 

 pestis. There is, on the other hand, a rather remarkable agree- 

 ment between the different strains except solely with regard 

 to glycerin fermentation. 



Under usual conditions dextrose, mannite, and levulose are 

 fermented regularly and fairly strongly. Maltose, arabinose, 

 galactose, and salicin are also fermented, but more irregularly 

 except under favorable conditions. A few strains ferment 

 glycerin. Dextrin, lactose, saccharose, rafRnose, adonite. 



