170 



A TEXTBOOK OF BOTANY 



[Ch. IV, 8 



Fio. 117. — A C'uloriscopc ; X h r l he two 

 Dewar bulbs have double walls with a vacuum 

 between (as familiar in "Thermos" bottles), and 

 hence prevent loss of heat. The respiring tissue to 

 be tested is divided into two parts, and placed in 

 the two flasks, but is immediately killed in one. 

 Thus the delicate thermometers are made to record 

 within a few hours the degree of heat released by 

 the respiration of the living tissues. 



liquid in the 

 flask is found to 

 contain a con- 

 siderable quan- 

 tity of alcohol, 

 together with 

 small amounts of 

 other substances 

 known to be 

 formed by the 

 activity of the 

 Yeast, which all 

 this time is in 

 vigorous growth 

 and multiplica- 

 tion. If certain 

 mineral salts, es- 

 sential to the 

 metabolism of 

 the Yeast, are 

 present, the pro- 

 cess continues 

 until the sugar 

 is exhausted, or 

 else until the in- 

 creasing quanti- 

 ties of alcohol in- 

 hibit the further 

 growth of the 

 Yeast. Thus, un- 

 der experimental 

 conditions, the 

 Yeast plant in 

 its growth fer- 

 ments sugar to 

 carbon dioxide 



