EXTRACTS OF PURE DRY YEAST FOR CULTURE 



MEDIA 



S. HENRY AYERS and PHILIP RUPP 



From the Research Laboratories of the Dairy Division, United States Department of 



Agriculture 



Received for publication August 16, 1919 



Dry yeast has been extensively used for the preparation of 

 media in these laboratories for the past five years with excellent 

 results; but has received little if any attention from other bac- 

 teriologists in this country. 



Eldredge and Rogers (1914) in 1913 used an extract from dry 

 yeast with peptone and phosphate for studying the fermenta- 

 tions of cheese cultures because they desired a sugar free broth 

 in which their cultures would grow readily. For the same reason 

 yeast peptone broth was used by one of the authors (Ayers, 1916) 

 during 1915 and is still being used in studying the fermentations 

 of the streptococci. This sugar free broth was found to be of 

 particular value in supporting the growth of pathogenic strepto- 

 cocci which would not grow in extract broth or meat infusion 

 broth from which sugar had been removed by fermentation. 

 Yeast peptone broth was also used by Miss Evans (1918) in a 

 study of the streptococci concerned in cheese ripening. 



Extracts from dry yeast have been used so successfully in other 

 bacteriological work in the Research Laboratories of the Dairy 

 Division that it is believed special attention should be given to 

 their possibilities. It is, therefore, the purpose of the writers to 

 mention briefly in this paper some of the ways in which yeast 

 extracts have been used in recent experiments. 



DRY FRESH YEAST 



In the work previously noted, an imported dry yeast prepara- 

 tion was used about which nothing was known as to the methods 

 of manufacture. The fact that, with peptone, it gave a broth 



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