THE ELEMENTS OF PLANT FOOD 41 



may be in the air, and if they find favorable conditions 

 of temperature and moisture, they will increase rapidly 

 in the substance that is adapted to their life. The 

 action of these organisms on glucose produces alcohol. 



Notes. Enzymes (also called soluble ferments, zymeses, and 

 diastases) are active, organic substances secreted by cells which have 

 the property, under certain conditions, of hastening chemical reactions 

 between certain bodies without entering into the composition of the 

 products which result. Enzymes are secreted in the ptyalin of the 

 saliva, in the gastric juice of the stomach, and the pancreatic juice. 

 These enzymes cause changes in the food we eat, rendering them more 

 easy to assimilate. Enzymes are also secreted by the cells of the yeast 

 plant and cause fermentation to take place. 



If a thick solution of glucose is placed in a glass and exposed to the 

 air, no change takes place. Fermentation requires the presence of 

 some enzymes. If then there is introduced into the solution some 

 vegetable matter containing nitrogen, the enzyme-producing organisms 

 have a favorable medium for development, and alcohol is produced. 

 Both the enzymes and the albuminous matter may be introduced directly 

 in the form of yeast. A portion of a yeast cake put into the glucose 

 solution will cause alcoholic fermentation to take place. 



There are other ferments adapted for growth in other substances than 

 sugar. The vegetable ferment that causes the souring of milk is called 

 a lactic ferment. Another ferment acts upon alcohol and produces 

 vinegar. This is called acetic ferment. Butyric fermentation is 

 caused by an organism in butter. 



Distillation. Alcohol is made in large quantities 

 from corn and from potatoes. The starch in the corn 

 and in the potato is changed into glucose by fermenta- 

 tion, and then the glucose is changed into alcohol. 

 A still is necessary for distilling and collecting the al- 

 cohol. A mash made of the corn or vegetable from 

 which the alcohol is to be made is allowed to ferment 

 till the alcohol is formed in it. The mash is then 



