92 S. HENRY AYERS AND PHILIP RUPP 



cately growing streptococci. The amount of reducing sugar 

 found would not give sufficient acid to account for the change in 

 pH previously noted so there was doubtless other fermentable 

 material present not determined as a reducing sugar. 



The yeast extract from dry fresh yeast made a good medium 

 for many bacteria but was of most value when used with peptone. 

 It was not, however, satisfactory for fermentation tests on ac- 

 count of the fermentable material present. In this connection, 

 it should be mentioned that both pressed yeast and yeast extracts 

 have been found by Ickert (1918) to be a cheap and suitable sub- 

 stitute for meat extract in ordinary media. 



DRY AUTOLIZED YEAST 



It is well known that yeast readily undergoes autolysis which 

 as Vansteenberge (1917) pointed out may operate in two ways. 

 The nitrogenous material undergoes proteolysis in which pep- 

 tones, amino acids, and other products are formed, while the 

 hydrocarbon material, principally glycogen, is transformed into 

 glucose, then into C0 2 and alcohol. 



Vansteenberge also showed that an extract from autolized 

 yeast contained much more nitrogenous material than a similar 

 extract from fresh yeast and that such an extract was a suitable 

 medium for the growth of yeast and lactic acid bacteria. 

 An extract of autolized yeast has been found by Dienert and 

 Guillerd (1919) to be a cheap and satisfactory medium for the 

 growth of B. coli. 



Kligler (1919) has recently advocated the use of yeast autoly- 

 sate as a culture medium. He used brewer's yeast which he 

 autolized in the laboratory. The use of brewer's yeast as he has 

 suggested presents two serious difficulties. First, it is difficult to 

 obtain fresh brewer's yeast in many parts of the country and 

 second, brewer's yeast undergoes autolysis so rapidly that if it 

 was shipped in a moist condition it would arrive at its destination 

 in various states of decomposition depending upon the time and 

 temperature during transit. It would doubtless be impossible 

 to make uniform media in different laboratories with such mate- 



