322 AGRICULTURAL CHEMISTRY 



cover the end of the tube. Place the flask on a warm sand-bath, 

 below 85 F., for half an hour. Observe the bubbles of gas given 

 off and the precipitate formed in the lime water. Do not overheat 

 the sand-bath. 



Questions, (i) What is yeast and what does it contain? (2) 

 What caused the gas to be given off? (3) From what was the gas 

 formed? (4) Write the reaction with Ca(OH) 2 . (5) What be- 

 comes of the alcohol ? 



444. Ferment Action and Food Digestion. The di- 

 gestion of food is carried on largely by the action of solu- 

 ble ferments. The digestive tract secretes a number of 

 these, which act upon the insoluble nutrients and change 

 them to soluble forms. In fact, the digestion of food is 

 dependent upon the action of the different ferments in the 

 digestive tract, as ptyalin in the saliva, pepsin in the 

 stomach, pancreatin in the duodenum, and diastase and 

 other ferments in the intestines. 



445. Ferments and Food Preservation. Preservation 

 of food is dependent upon prevention of ferment action. 

 The low temperature of cold storage is unfavorable to 

 the development of ferments. Sterilization is likewise 

 unfavorable. By means of heat, cold storage, chemicals, 

 and protection from the spores in the air, perishable food 

 products are preserved. Some ferments, however, are 

 not destroyed either by high or low temperatures. 



446. Ferments in Butter- and Cheese-flaking. The 



process of butter- and cheese-making is carried on with 

 the aid of ferments. Milk itself contains enzymes or 

 soluble ferments and, to a limited extent, is itself capable 

 of acting as a digestive fluid. The ripening of cream is 



