HYDROGEN-ION CONCENTRATION OF BROTH MEDIA 157 



components of broth media are in themselves complex compounds, 

 which in some cases, are relatively unstable and reactive. It has 

 long been noted that in the preparation of media precipitates 

 occur when certain amounts of acid or base are added. In some 

 cases precipitation occurs as soon as the acid or base is added, in 

 other cases autoclaving seems to be required to bring down the 

 material. Khgler (1917) has estabhshed certain zones of hydro- 

 gen-ion concentration for aqueous solutions of peptone within 

 which precipitation occurs, and has investigated the nature of 

 the precipitates themselves. In the acid range he beheves that 

 the material arises largely from protein substances as upon redis- 

 solving it gives reactions of proteoses and peptones, whereas in 

 the alkaline range it is made up largely of phosphates. It is 

 rather significant that the ranges of Ph in which we find the great- 

 est change in reaction upon sterilization and standing are those 

 within which precipitation is apt to occur during adjustment of 

 the media. 



The role of peptone in media is two-fold. It furnishes nitrog- 

 enous food in the form of protein split products (peptones, pro- 

 teoses, peptides, amino acids) and through its property of combin- 

 ing with acids and bases acts as a buffer. According to Rettger, 

 Berman, and Sturges (1916) and Davis (1917) American peptones 

 are lower in albumoses and higher in amino acids than Witte's, 

 some of those examined by the latter having two or three times 

 the content of amino acids. 



It seems quite certain that during autoclaving of culture media 

 the higher nitrogenous complexes are hydrolyzed to lower spHt 

 products. This would be particularly true in media adjusted in 

 the acid or alkaline ranges, inasmuch as acids. and bases act as 

 positive catalyzers of a protein hydrolysis. During the sphtting 

 of a protein by hydrolysis there occur marked changes in the 

 acidity or alkalinity of the solution in which the change takes 

 place. Sorensen (1912) has reported an experiment in which the 

 digestion of peptone by trypsin was carried out, measurements of 

 hydrogen-ion concentration and determinations of the increase 

 in formol-titrating material being made at intervals. The in- 

 crease in hydrogen-ion concentration did not stand in relation to 



