LOUIS FREEDMAN 21 



Na 2 HP0 4 and NaH 2 P0 4 for the alkaline range, and solutions 

 consisting of mixtures of acetic acid and sodium acetate, ac- 

 cording to Walpole 11 , for the acid range. With these standard 

 solutions, we used the following indicators : 



Phenol red, for PH 8.0 6.8 

 Brom thymol blue, for PH 7.66.0 

 Brom cresol purple, for PH 6.9 5.2 

 Methyl red, for PH 6.04.4 



Three-tenths cc. of the required indicator solution was added 

 to 10 cc. of the standard solution. The colored solutions were 

 then put into uniform test tubes and the tubes sealed. The 

 tests were made as follows : Duplicate tubes were prepared, each 

 containing 9 cc. of the D.I.-G.S. medium and 1 cc. of the protein 

 hydrolysate. One tube was inoculated with the streptococci and 

 the other kept sterile. Both tubes were incubated together. After 

 twenty-four hours, 0.3 cc. of the indicator necessary, which was 

 determined roughly by the amount of bacterial growth formed, 

 was added to each tube and the resulting color compared with the 

 standard tubes. 



As we used a control check for each test, we found this 

 method to be very convenient and fairly accurate for compara- 

 tive results. We have for convenience tabulated the results ob- 

 tained with our protein hydrolysates in their stimulating action 

 on the growth of streptococci, in tables Ila and b. 



TABLE II (a) 



Quantitative Effect of Protein Hydrolysates on the 

 Growth of Streptococci. 



PH of standard D.I.-G.S. solution = 7.3 



PH 



No. 'Hydrolysates of Animal Proteins. Growth after 



(1 cc. used in each test) incubation 



1. Casein (purified) HC1 hydrolysate + 5.8 



1 (a). (sterile control) 7.3 



2. Casein (purified) H 2 SO< hydrolysate + 5.3 



2 (a). (sterile control) 7.0 



3. Casein (technical) HC1 hydrolysate + 5.8 



3 (a). (sterile control) 7.3 



4. Lactalbumin 7.0 



4 (a). (sterile control) 7.3 



5. Filbrin 7.3 



5 (a). " (sterile control) 7.3 



