554 WILLIAM S. STURGES AND LEO F. EETTGER 



quirements. A pepsin-like enzyme was observed whose activity 

 depended upon a hydrogen ion concentration greater than pH 

 5.5. In ever}^ instance there were also present enzjTnes of a 

 tryptic nature, most active in a fairly alkaline medium. The 

 acid end of the range of the latter, however, overlapped the 

 alkaline end of the range of the former ferments and a digestion 

 (or autolysis) carried on in the pH zone common to both tended 

 to be much more complete than one carried out in the alkaline 

 range so often chosen for such experiments. 



Our knowledge of bacterial autolysis is as yet far from com- 

 plete, and the Uttle information which has been acquired is con- 

 fined, with very few exceptions, to the changes which take place 

 in the protein of the bacterial cell. In some instances the in- 

 vestigations have not gone beyond a morphological study, and 

 in very few cases were the changes determined by modern 

 chemical methods. 



There is considerable difference of opinion in regard to the 

 definition of the term "autolysis." The word has been variously 

 used to express changes in gross and microscopic appearance, 

 loss of vitality, changes in solubiUty and actual changes in 

 chemical composition. From a careful consideration of the 

 phenomena which Salkowski originally observed and for which 

 Jacobi first introduced this term, and in view of its extensive 

 usage in the biochemical field, the authors would define "autoly- 

 sis" as "the breaking down and solution of some of the essential 

 chemical constituents of the cell by agencies (enzymes) originat- 

 ing within the cell." As bacteria are composed mainly of proto- 

 plasm it may be assumed that in ordinary autolysis the hydrol- 

 ysis is chiefly of a proteolytic nature. It is for this reason that 

 the present investigation has been concerned wholly with the 

 changes which the proteins and related complex nitrogenous 

 substances undergo. 



The logical basis for any serious consideration of the phenom- 

 enon of autolysis must be a study of the chemical changes 

 involved. The hydrolysis of protein or protein-hke substances 

 consists in the decomposition of the more complex molecules 

 into simpler components. This constitutes a change in the 



