ITS PROPERTIES. 291 



gressive decomposition which it suffers from the action of ail 

 and water. 



Now when yeast is made to act on sugar, it is found that 

 after the completion of the transformation of the latter substance 

 into carbonic acid and alcohol, part of the yeast itself has dis- 

 appeared. 



From 20 parts of fresh yeast from beer, and 100 parts of 

 sugar, Thenard obtained, after the fermentation was completed, 

 13-7 parts of an insoluble 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 fermentation 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 condition should 

 have a similar action upon sugar ; and this is in reality the case. 

 Muscle, urine, isinglass, osmazome, albumen, cheese, gliadine, 

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

 have 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 putrefying animal and vegetable matters act as 

 peroxide of hydrogen does on oxide of silver, when they induce 

 bodies with which they are in contact to enter into the same 

 state of decomposition. The disturbance in the attraction of the 

 constituents of the peroxide of hydrogen effects a disturbance 

 in the attraction of the elements of the oxide of silver, the one 

 being decomposed on account of the decomposition of the 

 other. 



Peroxide of hydrogen is rapidly decomposed in contact with 

 moist fibrin of blood, an animal substance in a continuous state 

 of decomposition. The oxygen which it contained, in addition 

 to that necessary to form water, escaped with violent effer. 

 vescence. 



