OF FOOD. 



5 



Meat yields to warm water at 60 C. about 3 per cent, of 

 albuminous material and nearly as much extractive. On 

 boiling the aqueous extract, the albumin coagulates (as 

 scum), but when the boiling is long continued some of it 

 redissolves (Mulder). Consequently the quantity of albu- 

 minous material contained in bouillon, always small, varies 

 according to the mode of preparation. It may be increased 

 by the addition of a trace of hydrochloric acid to the 

 water used. Bouillon, beef tea, and other similar products 

 owe their value, partly to the gelatin, but chiefly to the salts 

 and extractive which they contain. "Liebig's Extract" 

 contains neither proteid nor gelatin. 



Meat, when roasted, retains its juice, which, from the 

 comparatively low temperature of the internal parts (indi- 

 cated by the colour) does not coagulate. The tenderness 

 which meat acquires by keeping is due to conversion of 

 some of its myosin into albummate. Cooking is useful, 

 not only as preparatory to digestion, but as destructive of 

 parasites and of morbid and septic products. 



Milk. All of the constituents of milk are of nutritive 

 value. Cream consists chiefly of casein and butter; Butter 

 contains, in addition to the ordinary fats (Palmitin, Stearin, 

 and Olein), about 2 per cent, of the glycerides of the 

 volatile acids; Biitter milk consists of sugar, casein and 

 salts ; Whey of sugar and salts; Cheese of casein with 

 variable quantities of butter, and of the products of de- 

 composition of both. Human milk contains less than 4 per 

 cent, of casein, between 3 and 4 per cent, of butter, and 

 from 4 to 5 per cent, of sugar. In Colostrum the casein is 

 partly replaced by serum albumin. Cows' milk contains 

 much more casein than human milk, but no more sugar : 

 consequently, when the former is diluted, as a substitute for 

 the latter, milk sugar (which as crystallized from whey 

 always contains calcic and potassic phosphates) must be 

 added. Cows' milk always contains a small percentage of 

 albumin. 



