FOOD. 



FOOD. 



Albumen or fibrin and gelatin, small propor- 

 tions of saline bodies, and a large quantity of 

 water, are found in them all. 



It often happens that the truly nutritious 

 part of food is so combined with or protected 

 by indigestible matters as to escape the solvent 

 powers of the stomach, unless previously pre- 

 pared and modified by various chemical and 

 mechanical agents. Indurated woody fibre, for 

 instance, or lignin, as chemists call it, will often 

 resist the joint action of the stomach and bow- 

 els, and p" ass through the alimentary canal with 

 scarcely any alteration. The husks of many 

 seeds and fruits are composed almost exclu- 

 sively of this material. This is the case with 

 the kernels of the apple, pear, &c. ; the seeds 

 of the currant, gooseberry, melon, and so on ; 

 the skin or husk of peas, beans, &c., and of 

 wheat, barley, and oats ; so that unless the 

 woody part is either broken down by the teeth 

 or previously removed, the food which it enve- 

 lopes is protected in some degree from the sol- 

 vent action of the secretions of the stomach. 

 This is a wise and curious provision in nature, 

 for birds in this way become the carriers of 

 seeds, which pass through them not only un- 

 digested, but even retaining their vegetative 

 powers ; and in this way uninhabited and ste- 

 rile portions of the globe may gradually become 

 clothed with verdure, and shrubs, and trees; 

 hence the advantage derived from bruising the 

 corn given to live-stock. Bones are highly 

 nutritive, but, unless broken into very small 

 fragments by the masticatory powers of the 

 animals which eat them, they too would elude 

 digestion. 



There is another important point in the his- 

 tory of food, which is, its ultimate composition. 

 Four elements only are principally concerned 

 in the production of the food of animals ; these 



| are carbon, hydrogen, oxygen, and nitrogen. 



I Among vegetable substances, gluten (including 

 vegetable albumen) is the only one which 

 abounds in nitrogen ; gum, sugar, starch, and 

 the rest, are constituted of carbon, hydrogen, 

 and oxygen only. There are two very singular 

 points in reference to the chemical history of 

 food: the one is, that no animal can subsist for 

 any length of time upon food which is destitute 

 of nitrogen ; and the other, that a certain mix- 

 ture of different food is absolutely essential. 

 Habit, as is well known, will do much in ac- 

 customing the stomach to particular descrip- 

 tions of food : many persons live exclusively, 

 or almost so, on vegetables, others on animal 

 matters, and particular kinds of diet are forced 

 on the inhabitants of many regions of the globe ; 

 but as far as we are concerned, a due mixture 

 of vegetable and animal matter is not only most 

 palatable, but most conducive to health. No- 

 thing is fit for food which has not already un- 

 dergone organization; and water, though an 

 essential part of the food of all animals, is ob- 

 viously not in itself nutritious, though it per- 

 forms the extremely important function of dis- 

 solving nutritive matter, so as to render it con- 

 veyable by the lacteals and other absorbents 



j into the blood. 



The subjoined table will serve to show the 



! comparative value of the principal cereal and 

 other grasses, legumes, roots, &c. (Davy, Elem. 



I Jig. Chem. 150.) 



I. Talk of the Quantities of Soluble or Nutritive Matters afforded by 1000 Parts of different 

 Vegetable Substances examined in their green state. 



499 



