ADVANCED PHYSIOLOGY 



yeasts bear very important relations to human health 

 and happiness. 



YEASTS 



Yeasts are abundant everywhere; they float in the air, are 

 found in water and are in and on the ground. Such yeasts 



are sometimes called wild 

 yeasts. Scientists have learned 

 to cultivate them in labora- 

 tories, and they may be 

 grown in great masses. A cake 

 of compressed yeast is simply 

 a cake of millions of these 

 tiny plants, all alive and ready 



FIG. 29 RECENTLY MIXED DOUGH, 



INOCULATED WITH YEAST, BUT 

 BEFORE THE YEAST HAS GROWN 

 (Conn, Bacteria, Yeasts and Molds). 



to grow if given proper food. 

 These are called cultivated 

 yeasts; but in reality the culti- 

 vated yeasts and the wild yeasts 

 are the same kind of plants. 

 When a cook wishes the 

 dough " to rise," she puts a 

 yeast cake in it, and the yeast, 

 growing in the dough, ferments sugar in the starch of the 

 fiour, producing bubbles of gas, which make the 



FIG. 30. THE SAME DOUGH 

 AFTER YEAST HAS GROWN AND 

 CAUSED THE DOUGH TO SWELL 

 BY THE ACCUMULATION OF GAS 

 (Conn, Bacteria, Yeasts and Molds), 



