HYDROGEN ION CONCENTRATION AND PROTEOLYSIS. 143 



microorganisms themselves are killed. Hankin^ showed that an extract 

 made from Bad. anthracis contains an enzyme which is capable of forming 

 albumoses from fibrin. Sirotinin ^ has proved that certain bacteria pro- 

 duce exo-enzymes. Brunton and MacFadj^en^ found that the secretion 

 of certain enzjTnes by a particular bacterium is influenced by the con- 

 stituents of the media in which it is cultivated, and also that its activity 

 is governed by the acids and alkahs present. Wood ^ extracted enzymes 

 from the culture media in which several known bacteria were cultivated. 

 Thus far these workers have dealt with the proteolytic activity of bacteria 

 qualitatively, and have noted some of the operating influences. It was 

 Fermi who attempted to determine quantitatively the proteolysis caused 

 by different bacteria. He measured the amount and rapidity of gelatin 

 solution. Besides gelatin, Fermi' experimented with other protein sub- 

 stances, such as fibrin, egg albumin, coagulated serum-albumin, using the 

 enzymes secreted by various bacteria; but he found that the greatest 

 acti\aty in proteolysis is secured in gelatin. His investigation is not 

 tenable because room temperatures fluctuate widely and cannot furnish 

 exact conditions of growth. The influence of the liquefying of gelatin by 

 heat upon proteolysis must make the results variable. There is an opti- 

 mum temperature for proteolysis as well as for the growth of micro- 

 organisms; consequently, only definite temperatures can be used for its 

 study. Eijkmann* employed milk agar in the study of different micro- 

 organisms. The results obtained, however, were only approximate. 

 Later, Abderhalden and Koelker^ and others introduced the polariscope 

 to determine the degree of proteolysis ; but this method is not well adapted 

 to general work on account of turbidity of growth and the slight degree 

 of polarization. With the development of protein chemistry it became 

 possible to ascertain quantitatively the cleavage products. Rosenthal 

 and Patai ^ investigated the proteolytic activity of streptococci, staphylo- 

 cocci and the colon group by the formol titration method of Sorensen, 

 which is yet to be discussed. 



QUESTIONS INVOLVED. 



The problems involved in the proposed investigation are presented 

 diagrammaticaUy. 



A brief explanation follows : — 



The object of this investigation is to study the influence of hydrogea 

 ion concentration of media upon the proteolytic activity of B. subiilis. 



After reviewing the previous literature it was necessary to consider the 

 following details of procedure: — 



1 Green, R! Fermentation. Cambridge Nat. Science Manual, 1899. 



* Proc. Roy. Soc, 46, 1889, 542. 



» Archiv. f. Hygiene, V. 10, 1, 1890; V. 14, 1, 1892. 



* Centralbl. f. Bakt., Abt. I, Bd. 29, U. 35. 



« ZeitBchr. f. Physiol. Chem., Bd. 51, 294, 1907. 



» Centralbl. f. Bakt. (Originale), Bd. 73, Heft 6, April, 1914, S. 406-412. 



