EXTRACTS OF PURE DRY YEAST 



95 



into peptones at about pH 4; tryptase, splitting peptones into 

 peptides at about pH 7.0; and ereptase, splitting peptides into 

 amino acids at about pH 7.8. It appears, therefore, that it 

 should be possible to control the process of yeast autolysis so 

 that dried preparations would contain various amounts of pep- 

 tones, peptides, and amino acids, according to the method of 

 autolysis. Such preparations should be valuable in studying 

 the nutrition of bacteria and should be relatively inexpensive. 



YEAST DIGESTED WITH ACID 



Other methods of obtained extracts from dried fresh yeast were 

 tried as, for example, heating with acid and alkali. The extract 

 of yeast treated with acid gave the best results and will be the 



TABLE 3 



One per cent yeast extract from : 



Dried fresh yeast 



Dried autolized yeast 



Dried fresh yeast treated with 

 acid 



TOTAL 

 NITROGEN 



per cent 



0.0209 

 0.0616 



0.0491 



AMINO 

 NITROGEN 



EXTRACT 



per cent 



0.0040 

 0.0274 



0.0069 



PROTEIN 

 OTHER 

 THAN 

 AMINO 

 AGIDS 



per cent 



0.1078 

 0.2192 



0.2692 



FERMENTABLE 

 MATERIAL 



Small amount 

 Trace 



More than in ex- 

 tract from dried 

 fresh yeast 



only one discussed. To obtain the extract, 10 grams of dried 

 fresh yeast were added to 400 cc. of distilled water together with 

 50 cc. N HCL. This was then heated in an autoclave at 14 lbs. 

 pressure for 30 minutes. After heating, 50 cc. of N NaOH was 

 added to the yeast extract which was allowed to cool before fil- 

 tering. A clear filtrate was obtained. The reaction which was 

 slightly above pH 7.0 was adjusted to pH 7.5. This yeast ex- 

 tract was made up to 1000 cc. with distilled water to make a 1 

 per cent solution. The extract when used with 1 per cent pep- 

 tone showed luxuriant growth with cultures of streptococci, but 

 from the change in pH 7.5 to about pH 5.7 it was evident that 



