CAUGHT IN THE CURD. FERMENTATION. 201 



effect of great heat, or sudden changes in the atmos- 

 phere, that there is not time for the butter particles to 

 rise to the surface, and they remain mixed up with the 

 curd. 



Nor does the serous or watery matter remain dis- 

 tinct or free from the mixture of particles of the cheesy 

 and buttery matters. It also holds in suspension some 

 alkaline salts and sugar of milk, to the extent of from 

 three to four per cent, of its weight. 



We have, then, 



Milk. 1 fr i f Buttery and cheesy residuum. 



Iskimmed milk. &r of milk. 



It may be stated, in other words, that milk is com- 

 posed chiefly of caseine, or curd, which gives it its 

 strength, and from which cheese is made ; a butyra- 

 ceous or oily substance, which gives it its richness ; a 

 sugar of milk, to which it owes its sweetness, and a 

 watery substance, which makes it refreshing as a beve- 

 rage ; together with traces of alkaline salts, from whence 

 are derived its flavor and medicinal properties ; and 

 that these constituents appear in proportions which 

 vary in different specimens, according to the breed 

 of the animal, the food, the length of time after parturi- 

 tion, etc. 



Milk becomes sour, on standing exposed to a warm 

 atmosphere, by the change of its sugar of milk into an 

 acid known as lactic acid ; and it is owing to this sugar, 

 and the chemical changes to which it gives rise, that milk 

 is susceptible of undergoing all degrees of fermenta- 

 tion, and of being made into a fermented and palatable 

 but intoxicating liquor, which, by distillation, produces 

 pure alcohol. This liquor is extensively used in some 



