FOOD 111 



then loss of appetite and digestive disturbance are not so 

 likely to follow the excessive administration of fat. The 

 fat, however, does not alter the digestibility of the food. 



The addition of salt to a diet is equally ineffectual in 

 causing a larger percentage of digestibility, though by 

 improving flavour it may cause a larger amount of food to 

 be consumed. 



THE HEAT AND WOEK PRODUCING POWER OP FOOD. 



At one time it was believed the theoretical heat producing 

 value of a food, was the best means of ascertaining its 

 nutritive usefulness. 



This is not correct, the question of the heat yielded by 

 food on combustion is of more theoretical than practical 

 importance, until we can make certain that what occurs in 

 the laboratory may also take place in the animal body. 



Proteid, fat, and carbo-hydrates, when burned yield heat ; 

 fat yields the most, carbo-hydrates the least. By means of 

 a calorimeter the amount of heat a definite quantity of 

 these substances is capable of yielding has been ascertained, 

 and is expressed as a heat unit. The heat required to 

 raise 1 gramme (15-432 grains) of water 1° C. (1-8° Fahr.) 

 equals one heat unit. 



1 oz. albumen yielded on oxidation 628 English heat units. 

 1 oz. fat „ ,, 1,017 ,, „ 



1 oz. starch „ ,, 504 „ „ 



1 oz. grape sugar „ ,, 368 „ „ 



A calorimeter and the animal body are not identical. 

 Proteid, for example, is not fully oxidised in the body, 

 quite one third of it passes away as urea, so that the heat 

 equivalent of proteid in the body is not the same as it is in 

 the laboratory experiment. In fact, observations show 

 clearly that the heat value of proteid may practically be 

 regarded as identical with starch, while that of fat is about 

 twice as great. 



When the heat units a substance can yield are known, 

 its mechanical value is calculated on the basis that the 



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