BIOCHEMICAL FEATURES 67 



acetate, methyl n-butyrate, and benzylacetate. While different de- 

 grees of hydrolysis were shown for the four esters, the comparative 

 ratio of the action of the two types of organisms on these esters 

 was of the same order in different lots of broth, although the abso- 

 lute values were not the same. As a rule, Type I organisms showed 

 a greater action than those of Type II, except in the case of 

 phenylacetate. 



CARBOHYDRATE FERMENTATION 



Important from a practical standpoint is the content in Pneu- 

 mococcus of carbohydrate-splitting enzymes, since the selective ac- 

 tion of the latter serves in the bacteriological differentiation of 

 this species from other species and genera of the family Coccaceae. 



Invertase, amylase, and inulase were first demonstrated in Pneu- 

 mococcus by Avery and Cullen (1920). 40 Finding that bile solu- 

 tions of pneumococci were unsuited to the purpose, the authors 

 used sterile extracts made by alternately freezing and thawing sus- 

 pensions of cells in balanced phosphate solutions at a pH of 6.2. 

 The enzymes were active within the limits pH 5.0 to 8.0, with an 

 optimum of 7.0. The acid death-point of pH 5.0 may be reached in 

 carbohydrate media, even when buffered with phosphates, if the 

 content of glucose exceeds 0.3 per cent (Avery and Cullen, Lord 

 and Nye 829 ). These authors agreed in ascribing carbohydrate fer- 

 mentations to intracellular or endoenzymes. The saccharolytic fer- 

 ments of Pneumococcus have a lower thermal death-point than the 

 protease or lipase, being destroyed at 55° in ten minutes. 



The enzymatic preparations freed of living cells hydrolyze su- 

 crose, starch, and inulin but, strange to say, fail to ferment glu- 

 cose, although in culture media the cleavage of this sugar into acid 

 is a definite and constant activity of the growth of Pneumococcus. 

 According to Hewitt, 643 the breakdown of glucose by Pneumo- 

 coccus is a less complex process than in the case of many other 

 organisms. Of the glucose constantly disappearing from such cul- 

 tures, about 78 per cent was recovered by Hewitt as lactic acid. 



