ACTION OF HEAT ON MILK 247 



such as carbon dioxide, hydrochloric, and other acids, or 

 by the addition of soluble calcium salts, no really char- 

 acteristic Cheddar, Cheshire, or other hard cheese has yet 

 been made from strongly heated milk. 



As stated previously heating destroys the normal 

 enzymes of milk. There is little doubt that the coagula- 

 tion of the albumen, the changes in the solubility of the 

 casein and calcium salts, and the destruction of the 

 enzymes render the milk less digestible and reduces its 

 nutritive qualities. 



Ex. 123. Mount a drop of fresh milk and one of the same 

 sample after being boiled. Examine with a f in. and in. objec- 

 tive and compare the arrangement of the fat globules in each. 



Ex. 124. Take 200 c.c. of fresh milk and divide it into two 

 parts : boil one of these and then cool it. Taste both. 



Add 10 c.c. of a weak solution of commercial rennet (5 of 

 rennet in 50 of water) to the boiled and the unboiled samples in 

 small beakers. 



Note the time taken to curdle each : the exact point can be 

 determined by scattering some pieces of charcoal scraped from 

 the end of a burnt match on the surface of the milk and stirring 

 with a glass rod : the floating particles stop at once when 

 coagulation occurs. 



Examine the curd produced : which is the firmest in texture ? 



