EXTRACTS OF PURE DRY YEAST 



93 



rial. The use of dry fresh yeast seems to overcome these 

 difficulties. 



Our object in obtaining an autolized yeast was not so much 

 to increase the protein content of the extract as to eliminate the 

 fermentable material. A dry autolized yeast was prepared by 

 one of the yeast manufacturers in accordance with our sugges- 

 tions. Fresh yeast was autolized for twenty-three hours at a 

 temperature of from 45° to 50°C, then dried at a low tempera- 

 ture. A medium made of a 1 per cent extract of this dry auto- 

 lized yeast and 1 per cent peptone adjusted to pH 7.4 proved to 

 be satisfactory for growth of many streptococci and the change 

 in the hydrogen ion concentration was from pH 7.4 (control) to 

 pH 7.0. This slight change in acidity showed that there was 



* Moisture in dry autolized yeast 5.96 per cent. 



some fermentable material left after autolysis but not enough to 

 interfere in any way with fermentation tests. The figures in 

 table 2 show an analysis of the extract. 



From a comparison of the figures in tables 1 and 2, it is appar- 

 ent that the 1 per cent extract from autolized yeast contained 

 about twice as much protein material (not including amino acids) 

 and about seven times as much amino nitrogen as the 1 per cent 

 extract from dry fresh yeast. 



To us, the most interesting and valuable feature was the re- 

 duction in fermentable material. No figures on reducing sugar 

 are given in table 2 because of substances present in the extract 

 from autolized yeast which interfered with the sugar test. The 

 changes in pH by bacterial growth, however, showed conclusively 

 that fermentable material was greatly reduced, in fact, to a 

 negligible amount. 



