CHAPTER IV 



FERMENTATION AND GERM DISEASES 



BEFORE food can be absorbed in the body it must be digested. 

 We shall study the details of digestion later, but before taking 

 them up, we must learn a little about the general process. 



The changes in food during diges- 

 tion belong to a type of activities 

 known as fermentation. It is dif- 

 ficult to define the word fermen- 

 tation, and we can best learn its 

 meaning through illustrations. 



TYPES OF FERMENTATION 



Alcoholic Fermentation. If to a 



solution of sugar a little yeast is 

 added, an active change soon be- 



\-\me\rto\et ms - ^he sugar disintegrates and 



FIG. 26. A FERMENTING turns into alcohol and carbon 

 SOLUTION dioxid gas. The sugar does not 



change spontaneously but only 



after the yeast is added, and the 



process continues until the sugar is used up. The micro- 

 scope shows yeast to be a minute living plant; Fig. 27. 

 While the sugar is fermenting, 

 the yeast grows and multiplies, 

 fermentation being a result of 

 its growth. If the yeast is 

 boiled, it is killed and can 

 no longer excite fermentation. 

 Since this yeast is a living plant FIG. 27. GROWING YEAST PLANTS 



.. i i 11 i Showing the method of formation of 



it can properly be called an bud s on the sides of the ceils, 



62 



