176 



The Philippine Journal of Science 



1916 



Acid production in serum bouillon. — Another question to be 

 determined was whether unsatisfactory results with serum 

 waters were due to limitation of growth on account of the sim- 

 plicity of the medium, or to the possibility that the serum itself 

 actually exercises a restraining effect. If the latter were the 

 case, sugar peptone-water with varying concentrations of added 

 serum should show differences in fermentation. A quantity of 

 dextrose peptone-water was separated into five lots, to four of 

 which Berkefeld-sterilized horse serum was added in various 

 concentrations. These and a control set without serum were 

 inoculated, using all ten strains of B. pestis. Titrations were 

 made with N/40 sodium hydroxide, after six days' incubation in 

 this case. The results appear in Table X. 



Table X. — Acid production in dextrose peptone-water containing various 

 amounts of filter-sterilized horse serum. 



Strain. 



Serum. 



Control 

 without 

 serum. 



0.2%. 



1.0%. 



5.0%. 



10. 0%. 



A .. 



2.65 

 2.6 

 2.6 

 2.6 

 2.2 

 2.4 

 2.5 

 2.65 

 2.2 

 2.35 

 ( 0.6 

 1 0.75 



2.5 



2.6 



2.55 



2.55 



2.4 



2.65 



2.75 



2.75 



2.2 



2.4 



0.6 



0.8 



2.75 



2.65 



2.75 



2.65 



2.65 



2.7 



2.6 



2.75 



2.5 



2.65 



1.05 



2.5 

 2.6 

 2.8 

 2.66 

 2.35 

 - 2.5 

 2.4 

 2.8 

 1.8 

 2.5 

 1.3 

 0.95 



2.6 



2.3 



2.66 



2.55 



2.25 



2.25 



2.5 



2.25 



2.0 



2.15 



0.66 



0.19 



B .... 



C . . 



D . . 



E . . 



p .... 



G 



H 



I 



J : 



Uninoculated controls .. 







No depression of fermentation is demonstrated in these cul- 

 tures, indicating that serum per se, in these percentages at least, 

 is not inhibitory, despite the fact that the amount of growth 

 was somewhat less than in dextrose peptone-water without serum. 



Influence of added nutrient on the reaction with Hiss's serum 

 waters. — Since serum per se appears not to have an inhibitory 

 effect, the effect of adding simple nutrient substances to the 

 serum-water stock was investigated. Beef extract alone proved 

 to be of no value. Peptone, if added in 1 per cent concentration 

 to the previously heated serum, gives, upon reheating, a soft 

 jelly, as described by Buerger, (19) which physically is not the 

 same as Hiss's medium. Making the original serum water one 

 part of serum to four of water and adding 0.5 per cent of peptone 

 after the primary heating gives an enriched medium which is 



