184 MASS. EXPERIMENT STATION BULLETIN 167. 



SUMMARY AND CONCLUSIONS. 

 Part I. 



1. The determination of "true reaction" in such a bacteriologic culture 

 medium as was used in the investigation can be made successfully by 

 means of the hydrogen electrode. 



2. Sorensen's formol titration method gives very satisfactory results 

 in determining the rate of proteolysis. 



3. Medium IV. seems very suitable for the determination of hydrogen 

 ion concentration and proteolysis in the case of B. subtilis. In order to 

 secure a fixed chemical and physical factor it is advisable to boil it for an 

 hour or place it in an autoclave for tliirty minutes or longer, under 15 

 pounds' pressure. 



4. The desired hydrogen ion concentration in the medium is obtained 

 by the aid of the colorimetric method, avoiding sterilization after the 

 addition of acid or alkali. 



5. Ph = 9-43 seems to have an inhibitory action upon B. subtilis, while 

 Ph's below 4.18 and above 9.43 have a germicidal effect. 



6. The minimum, optimum and maximum Ph for B. subtilis are as 

 follows : — 



Minimum, between Ph = 4 and Ph = 5. 

 Optimum, between Ph = 7.5 and Ph = 8.5. 

 Maximum, between Ph = 9 and Ph = 10. 



7. An alteration of the hydrogen ion concentration in the medium by 

 B. subtilis occurred between Ph = 4.18 and Ph = 9.43. 



8. B. subtilis produced a tryptic-like enzyme which is endo-cellular. 

 From the foregoing summary the relation between the hydrogen ion 



concentration in the medium and the proteolytic activity of B. subtilis 

 may be concluded as follows: certain hydrogen ion concentrations meas- 

 ure the exact influence both inhibitory and prohibitory, and indicate the 

 exact limits of the proteolytic activity of B. subtilis. Further, the hydrogen 

 ion concentrations of the medium converged toward the optimum as 

 proteolysis proceeded. 



Part II. 



1. Streptococcus enjsi-pelatis, the virulent strain, multiplied much more 

 rapidly in the broth than Streptococcus lacticus, the nonvirulent strain. 



2. A difference both in degree and rate of proteolysis is evident; Strepto- 

 coccus erysipelatis is much more active and vigorous than Streptococcus 

 lacticus. 



3. The optimum hydrogen ion concentration for proteolysis differs, 

 as follows: — 



Ph =7.62 or ( li) =2.40 XIO"* for Streptococcus erysipelatis. 

 Pii=7.02 or (li) =9.55X10'^ for Streptococcus lacticus. 



