DOMESTIC ECONOMY, HYGIENE, DIETETICS. 



367 



sustains such action. It is essential to the 

 idea of a food that it support or increase vital 

 actions; whilst medicines usually may lessen, 

 increase, or otherwise modify some of them. 

 " Foods are derived, " says Dr. Edward Smith, 

 "from all the great divisions of nature and 

 natural products, as earth, -water, and air, 

 solids, liquids, and gases; and from substances 

 which are living and organic, or inanimate and 

 inorganic. The popular notion of food as a 

 solid substance derived from animals and veg- 

 etables, whilst comprehensive is too exclusive, 

 since the water which we drink, the air which 

 we breathe, and certain minerals found in the 

 substance of the earth, are, adopting the defi- 

 nition given, of no less importance as foods. 

 It is, however, of great interest to note how fre- 

 quently all these are combined in one food, and 

 how closely united are substances which seem 

 to be widely separated. Thus water and min- 

 erals are found in both flesh and vegetables, 

 whilst one or both of the components parts of 

 the air, viz., oxygen and nitrogen, are dis- 

 tributed through every kind of food which is 

 alone capable of sustaining life. Hence, not 

 only may we add food to food to supply the 

 waste of the body, but we may within certain 

 limits substitute one for another as our appe- 

 tites or wants demand. . . . Further, 

 there seems to be an indissoluble bond existing 

 between all the sources of food. There are 

 the same classes of elements in flesh as in flour, 

 and the same in animals as in vegetables. 



" The vegetable draws water and minerals 

 from the soil, whilst it absorbs and incorporates 

 the air in its own growth, and is then eaten 

 to sustain the life of animals, so that animals 

 gain the substances which vegetables first ac- 

 quired. But in completing the circle the veg- 

 etable receives from the animal the air (car- 

 bonic acid) which was thrown out in respira- 

 tion, and lives and grows upon it ; and at 

 length the animal itself in whole or in part, 

 and the refuse which it daily throws off, be- 

 come the food of the vegetable. Even the very 

 bones of an animal are by the aid of nature or 

 man made to increase the growth of vegetables 

 and really to enter into their structure ; and 

 being again eaten, animals may be said to eat 

 their own bones, and live on their own flesh." 

 It will be seen from this that animal and veg- 

 etable foods contain precisely the same ele- 

 ments though in different combinations. At 

 the same time they differ sufficiently to make 

 a due proportion of each necessary to perfect 

 nutrition. One sterling point of difference is, 

 that nitrogen constitutes a much larger per- 

 centage of animal bodies than of vegetables. 

 Nitrogen is one of the most important ele- ; 

 ments of food; only such substances as con-| 



tain it can efficiently produce flesh or repair 

 wasted tissue. So important is this distinction, 

 in fact, that one of the divisions of food most 

 generally recognized by physiologists is into 

 nitrogenous and non-nitrogenous, or, as Lie- 

 big termed them, the flesh-forming and the 

 heat-producing. Both kinds are essential to 

 the maintenance of life, and it is because veg- 

 etables as a whole are deficient in nitrogen 

 that the highest degree of bodily vigor cannot 

 be kept up by them alone. 



It is understood that the structures of the 

 body are in a state of continual change, 

 so that atoms which are present at one hour 

 may be gone the next, and when gone the 

 structures will be so far wasted, unless the proc- 

 ess of waste be accompanied by renewal. But 

 the renewing substance must be of the same 

 nature as that wasted, so that bone shall be re- 

 newed by the constituent elements of bone, 

 and flesh by those of flesh. This is the duty 

 assigned to food, to supply to each part of 

 the body the very same kind of material that 

 it lost by waste. As foods must have the 

 same composition as the body, or supply some 

 such other materials as can be transformed 

 into the substances of the body, it is desirable 

 to gain a general idea of what these substances 

 are. The following is a summary of the prin- 

 cipal materials of which the body is com- 

 posed : 



Flesh, in its fresh state, contains water, fat, 

 fibrin, albumen, besides compounds of lime, 

 phosphorus, soda, potash, magnesia, silica, and 

 iron, and certain extractives, whose nature is 

 unknown. Blood has a composition similar in 

 elements to that of flesh. 



Bone is composed of cartilage, fat, and salts 

 of lime, magnesia, soda, and potash, combined 

 with phosphoric and other acids. 



Cartilage consists of chondrin, from which 

 gelatine is formed, with salts of soda, potash, 

 lime, phosphorus, magnesia, sulphur, and iron. 



The brain is composed of water, albumen, 

 fat (so-called), phosphoric acid, osmazome, 

 and salts. 



The liver consists of water, fat, and albu- 

 men, with phosphoric and other acids, in con- 

 junction with soda, lime, potash, and iron. 



The lungs are formed of a substance called 

 connective tissue, from which gelatine is formed 

 by prolonged boiling, albumen, a substance 

 analogous to casein, various fatty and organic 

 acids, with salts of soda and iron, and water. 



Bile consists of water, fat, resin, sugar, fatty 

 and organic acids, cholesterin, and salts of 

 potash, soda, and iron. 



Hence, it is requisite that the body should 

 be provided with salts of potash, soda, lime, 

 srpgnesia, sulphur, iron, and manganese, as 



