rrs PROPERTIES. 317 



sion must be allowed to cool in contact with the air, 

 and to remain some time exposed to its action. When 

 introduced into a solution of sugar in this state, it 

 produces a brisk fermentation ; but without previous 

 exposure to the air, it manifests no such property. 



The infusion absorbs oxygen during its exposure 

 to the air, and carbonic acid may be found in it after 

 a short time. 



Yeast produces fermentation in consequence of the 

 progressive decomposition, which it suffers from the 

 action of air and water. 



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

 found, that after the transformation of the latter 

 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, Thmard obtained, after the fermen- 

 tation 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 prop- 

 erties 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 ex- 

 cites fermentation by being itself in a state of de- 

 composition, all other matters in the same condition 

 should have a similar action upon sugar ; and this is 

 in reality the case. Muscle, urine, isinglass, osma- 

 zome,* albumen, cheese, gliadine, gluten, legumin, 

 and blood, when in a state of putrefaction, have all 

 the power of producing the putrefaction, or fermen- 

 tation of a solution of sugar. Yeast, w^hich by con- 

 tinued washing has entirely lost the property of in- 

 ducing fermentation, regains it when its putrefaction 



* An extractive animal matter on which the peculiar flavor of broth 

 is supposed to depend ; hence its name, from the Greek for odor and 

 broth. 



27* 



