FERMENTATION 323 



the result of the action of the lactic acid ferment which 

 changes the lactose (milk-sugar) into lactic acid. In 

 cheese-making, the rennet used for coagulating the milk 

 contains a number of ferments which take an important 

 part in the process. The flavor and odor of butter as 

 well as of cheese are the results of ferment action. In 

 butter- and cheese-making, it is the object to control the 

 action of the desirable ferments and to prevent the unde- 

 sirable ones from developing. Ropy milk, red spots in 

 cheese, and floating curds in cheese-making, are all 

 caused by fermentation. Butyric acid, one of the pro- 

 ducts found in foul milk and butter, is caused by the 

 butyric acid ferment. Milk is exceedingly susceptible to 

 the action of ferments. 



Experiment 76. Lactic fermentation. Place 5 grams milk-sugar, 

 100 cc. water, 5 cc. skim milk, and two or three crystals of sodium 

 phosphate in a flask. Leave the flask uncorked in the desk for 

 twenty-four hours. Then add a few drops of phenolphthalein in- 

 dicator, and determine the amount of lactic acid, i cc. alkali = 

 0.009 gram acid. 



Questions, (i) Why was milk used in this experiment? (2) 

 What was produced from the milk-sugar ? (3) Why was sodium 

 phosphate used? (4) How much acid was produced? 



447. Disease- Producing Organisms. Many diseases 

 are caused by the action of micro-organisms. The dis- 

 ease-producing organisms or bacteria invade the body 

 and rapidly multiply, living upon the fluids and tissues 

 of the body and producing poisonous products. Typhoid 

 fever, smallpox, diphtheria, tuberculosis, cholera, and 

 many other diseases are caused by specific bacteria. The 

 products produced by the action of the organism are 



