142 PHYSIOLOGY FOR THE LABORATORY. 



b. The sterilization of milk. 



1. Recall experiment D. I. How long did the 

 boiled milk keep sweet? How does boiling 

 affect the taste of milk? If the milk is 

 heated hot enough to kill all the infectious 

 germs, a scum appears on the top which is 

 the albumin of the milk coagulated by heat. 

 A boiled taste is also acquired which is 

 objectionable to some persons, though very 

 pleasant to others. Milk thus heated is a 

 little less digestible than fresh milk. If a 

 high degree of heat is used, the sugar is 

 scorched, and this forms a brown sediment 

 on the bottom of the dish. 



c. The Pasteurization of milk. 



Materials. Milk. Water. 



Apparatus. Pasteurizing apparatus or tin pail. Thermometer. 

 Bunsen burner. Stand. Bottles. Cotton-batting. 



The Pasteurization of milk may be easily done in any 

 home. 



Fill one or more bottles nearly full of milk and plug 

 with dry, clean cotton-batting. The apparatus for Pas- 

 teurizing consists of a large tin pail which has a false tin 

 bottom perforated with holes. The cover should fit tightly 

 and have a thermometer held in place by a cork in an 

 opening. Place the bottles in an upright position in the 

 pail and fill the pail with enough water to rise above the 

 milk in the bottles. Close the pail and heat over a Bunsen 

 burner until the water is 155 F. (if in winter) or 180 

 (in summer). Then remove the pail and keep tightly cov- 



