178 The Philippine Journal of Science me 



of bacterial fermentation. Bacillus coli, for instance, as shown 

 by Browne, (20) has a similarly uniform maximal point, which 

 lies between 2.1 and 2.4 per cent in dextrose and somewhat 

 lower with some sugars and is not raised by increase in sugar 

 present, or in the total amount of medium, or by increase in 

 initial acidity. Streptococci are quite different in that the max- 

 imal point of acid toleration differs greatly in different strains. 

 Broadhurst's figures, (21) obtained from sugar-free, meat-infusion 

 cultures, ranged between 1.5 and 8.5 per cent. In a beef -extract 

 broth series (22) the highest that she obtained was 2.3 per 

 cent as compared with 5.0 and 5.2 per cent with parallel in- 

 fusion broths, though with meat-extract broths Fuller and Arm- 

 strong(23) obtained much higher figures. Hopkins and Lang(24) 

 concluded that — 



Fermentation by a given streptococcus ceases when a certain acidity is 

 reached, irrespective of how much acid must be formed to produce this 

 acidity. 



So far as can be learned, the maximum acid production by 

 B. pestis has not previously been noted, although the limit of 

 primary acidity of media permitting the growth of the organism 

 has been studied. Wladimiroff and Kressling(25) found that the 

 addition of small amounts of acid diminished the amount of 

 growth, 3 per cent of normal hydrochloric acid causing complete 

 inhibition. Lactic acid was better tolerated, 5 per cent being 

 the maximum. Pakes and Joseph (26) found the point of inhibi- 

 tion of growth to be as high as 4.0 to 4.5 per cent. My results, 

 using sugar bouillons of different degrees of acidity, do not 

 coincide with this, as there was little growth and no increase 

 in end reaction with media primarily 2.5 per cent acid or above, 

 hydrochloric and lactic acids having identical limits. 



It is shown that the maximum acidity produced by B. pestis 

 in beef -extract bouillons ranges between 2.5 and 3 per cent. This 

 seems to be the same for all strains, although (see particularly 

 Table V) a strain may have a slightly lower maximum point 

 with one sugar than with another, due possibly to the special 

 nature of the end products. In some cases (see Table VI) 

 all strains uniformly show this feature, which has often been 

 noted in carbohydrate-fermentation studies. 



Similarly to Bi-oadhurst's results with streptococci, veal- 

 infusion broths permit, for some reason not determined, a greater 

 accumulation of titrable acid before fermentation is inhibited. 

 This seems probably due to differences in the nature of secondary 

 end products. The figures obtained in the series detailed in 



