FOODS. 



about Toir<ro f an i ncn i n diameter. Each globule is supposed by 

 some observers to be surrounded by a thin albuminous envelope, 

 which enables it to maintain the discrete form. Others deny the 

 existence of such a membrane. The chief proteid constituent of 

 milk, caseinogen, is held in solution by the presence of phosphate of 

 lime. On the addition of acetic acid or sodium chlorid up to the 

 point of saturation the caseinogen is precipitated^*, such and may be 

 collected by appropriate chemic methods. When taken into the 

 stomach, caseinogen is coagulated; that is, it is separated into casein 

 or tyrein and a small quantity of a new soluble' proteid. This change 

 is brought about by the presence in the gastric juice of a special 

 ferment known as rennin or pexin. 



The fat of milk is more or less solid at ordinary temperatures. 

 It is a combination of olein, palmitin, and stearin, with a small quan- 

 tity of butyrin and caproin. When milk is allowed to stand for some 

 time, the fat-globules rise to the surface and form a thick layer known 

 as cream. WKgn subjected to the churning process, the fat-globules 

 run together and form a coherent mass butter. 



Lactose is the particular form of sugar found in milk. In the 

 presence of Bacillus acidi lactici, the lactose is decomposed into 

 lactic acid and carbon dioxid, the former of which not only imparts 

 a sour taste to the milk, but causes a precipitation of the caseinogen. 



Ghe chief salt found in milk is phosphate of lime, and this is the 

 def source of this agent in the formation of bones. 



Eggs are also to be regarded as compJte^natural.loods, inasmuch 

 as they contain all the necessary food principles. The analysis 

 given in the above table represents the composition of the entire egg. 

 The white of the egg contains 12 per cent, of proteid and 2 per cent, 

 of fat. The yolk, however, contains 15 per cent, of proteid and 30 

 per cent, of fat. 



Composition of Cereal Foods. The average composition of 

 the principal cereals is shown in the following table : 



That the cereals are most important and useful articles of diet is 

 evident from their composition, consisting, as they do, of proteids 

 and carbohydrates in large proportion. Owing to the cellulose or 



