246 ELEMENTS OF PHYSIOLOGY 



one thirtieth of the proteid in meat escapes digestion. A 

 pound of fat requires three times as much oxygen in its 

 oxidation as a pound of sugar, and therefore yields three 

 times the heat and energy. The digestibility of fat is in- 

 creased by the fact that it ferments with difficulty, while 

 sugar and starch ferment more easily. Meat should be 

 thoroughly cooked to avoid the danger of diseases from 

 the trichina and other parasites. 



441. Milk of cows is suited for calves, and was intended 

 to be obtained by sucking and to be swallowed gradually. 

 It contains too large a proportion of proteid for infants, 

 and therefore water is added. The casein or proteid part 

 is coagulated in flakes by the rennin, and when a child 

 throws up coagulated milk, it does not mean that it is suf- 

 fering from indigestion, although it may sometimes mean 

 that it is being overfed. The tendency of milk to pro- 

 duce " biliousness " and constipation in some persons may 

 be explained as follows : when adults drink sweet milk 

 rapidly, especially toward the end of the meal, when much 

 acid is present in the stomach, the acid coagulates the 

 casein into large lumps of curd, which may seriously dis- 

 turb digestion, for milk was not intended to be drunk rap- 

 idly. Heat retards the production of acid in the gastric 

 juice and increases the secretion of rennin. If taken 

 before meals, hot and slowly, milk will agree with those 

 who have found it to produce indigestion. Buttermilk is 

 one of the most digestible of foods. 



442. Cheese is a concentrated food, and is one of the 

 cheapest although not one of the most digestible forms of 

 proteid. 



Does a pound of eggs contain more or less nourishment 

 than a pound of meat ( 434) ? At usual prices, which 

 is more economical, eggs or meat (see Table, 434) ? 



443. Meat Extracts. Researches concerning the nutri- 

 tive value of meat extracts, show that in none of them is a 



