96 S. HENRY AYERS AND PHILIP RUPP 



the acid treatment had increased the fermentable material. This 

 was also indicated by the sugar analysis which, however, did not 

 give consistent results, due to interfering substances. Analysis 

 further showed that the extract made from acid treated yeast 

 was somewhat different from the extract from either the dry fresh 

 yeast or the dry autolized yeast. The difference is shown in 

 table 3. 



The most noticeable difference between the three yeast ex- 

 tracts was the increase of amino acids and total nitrogen in the 

 autolized yeast extract over the fresh yeast extract and the in- 

 crease in protein (other than amino acids) in the acid treated 

 yeast extract without much increase in amino nitrogen. 



Extracts made from yeast treated with acid may give good 

 results in many lines of bacteriological work where the presence 

 of fermentable material is not undesirable. 



YEAST DIGESTED WITH PEPSIN 



An extract was also made with dry fresh yeast which was partly 

 digested with pepsin. Ten grams of dry yeast was added to 100 

 cc. of distilled water with 0.1 gram of pepsin. Sufficient HCL 

 was then added to bring the reaction to about pH 4.4. The mix- 

 ture was then incubated at 40°C. for twenty-four hours, steamed 

 for thirty minutes, filtered, diluted to 100 cc. with distilled water, 

 and the reaction adjusted to pH 7.5. This extract without pep- 

 tone supported the growth of delicately growing streptococci so 

 well that the value of this kind of yeast extract appears promis- 

 ing for many purposes other than fermentation tests. 



SUMMARY AND CONCLUSIONS 



The value is emphasized of using extracts made from dried pure 

 yeast, that is, yeast which has been washed and then dried at a 

 low temperature without the addition of starch or other fillers. 

 This extract may be used alone or as a basis for more complicated 

 media when necessary. 



Extracts of pure yeast contain, besides amino acids and other 

 proteins, fermentable material in small amounts, probably pres- 



