254 YEAST OR FERMENT, 



substance into carbonic acid and alcohol is com- 

 pleted, part of the yeast itself has disappeared. 



From 20 parts of fresh yeast from beer, and 100 

 parts of sugar, Thenard obtained, after the fer- 

 mentation was completed, 13*7 parts of an insolu- 

 ble residue, which diminished to 10 parts when 

 employed in the same way with a fresh portion of 

 sugar. These ten parts were white, possessed of 

 the properties of woody fibre, and had no further 

 action on sugar. 



It is evident, therefore, that during the fermenta- 

 tion of sugar by yeast, both of these substances 

 suffer decomposition at the same time, and disappear 

 in consequence. But if yeast be a body which 

 excites fermentation by being itself in a state of 

 decomposition, all other matters in the same condi- 

 tion should have a similar action upon sugar ; and 

 this is in reality the case. Muscle, urine, isin- 

 glass, osmazome, albumen, cheese, gliadine, gluten, 

 legumin, and blood, when in a state of putrefaction, 

 have all the power of producing the putrefaction, 

 or fermentation of a solution of sugar. Yeast, 

 which by continued washing has entirely lost the 

 property of inducing fermentation, regains it when 

 its putrefaction has recommenced, in consequence 

 of its being kept in a warm situation for some 

 time. 



Yeast and putrifying animal and vegetable matters 

 act as peroxide of hydrogen does on oxide of silver, 



