324 OF DIGESTION AND NUTRITIVE ABSORPTION. 



This is consistent with the teachings of experience respecting the fattening of 

 cattle ; for it is well known that this may bfe accomplished much sooner, if the 

 animals are shut up in a warm dwelling and covered with cloths, than if they 

 are freely exposed in the open air. Now the condition of Man may be regarded 

 as intermediate between these two extremes. The construction of his digestive 

 apparatus, as well as his own instinctive propensities, point to a mixed diet as 

 that which is best suited to his wants. It does not appear that a diet composed 

 of ordinary vegetables only, is favourable to the full development of either 

 his bodily or mental powers ; but this cannot be said in regard to a diet of 

 which bread is the chief ingredient, since the gluten it contains appears to be 

 as well adapted for the nutrition of the animal tissues, as does the flesh of 

 animals. On the other hand, a diet composed of animal flesh alone is the least 

 economical that can be conceived ; for, since the greatest demand for food is 

 created in him (taking a man of average habits in regard to activity and the 

 climate he inhabits), by the necessity for a supply of carbon and hydrogen to 

 support his respiration, this want may be most advantageously fulfilled by the 

 employment of a certain quantity of non-azotized food, in which these ingre- 

 dients predominate. Thus it has been calculated, that some fifteen pounds of 

 flesh contain no more carbon than four pounds of starch. A savage with one 

 animal and an equal weight of starch, could support life for the same length 

 of time, during which another restricted to animal food, would require five 

 such animals, in order to procure the carbon necessary for respiration. Hence 

 we see the immense advantage as to economy of food, which a fixed agricul- 

 tural population possesses over the wandering tribes of hunters, which still 

 people a large part both of the old and new continents. The mixture of the 

 azotized and non-azotized compounds (gluten and starch), that exists in wheat 

 flour, seems to be just that which is most useful to Man ; and hence we see 

 the explanation of the fact, that, from very early ages bread has been regarded 

 as the "staff of life." In regard to the nutritious properties of different arti- 

 cles of vegetable food, these may be generally estimated by the proportion of 

 azote they contain ; which is in almost every instance less than that existing in 

 good wheat flour. 



434. Besides these substances, there are certain Mineral ingredients, which 

 may be said to constitute part of the food of Animals; being necessary to'their 

 support, in the same manner as other mineral substances are necessary to 

 the support of Plants. Of this kind are common salt, and also phosphorus, 

 sulphur and lime, either in combination or separate. The uses of Salt are 

 very numerous and important. It consists of two substances of opposite 

 qualities, muriatic acid and soda; and the former is the essential ingredient in 

 the gastric juice ; whilst the latter performs a very important part in the pro- 

 duction of bile. Phosphorus is chiefly required to be united with fatty matter, 

 to serve as the material of the nervous tissue ; and to be combined with oxygen 

 and lime, to form the bone-earth, by which the bone is consolidated. Sulphur 

 exists in small quantities in several animal tissues ; but its part is by no means 

 so important as that performed by phosphorus. Lime is required for the con- 

 solidation of the bones, and for the production of the shells and other hard 

 parts that form the skeletons of the Invertebrata. To these ingredients we 

 may also add Iron, which is a very important element in the red blood of Ver- 

 tebrated animals. These substances are contained, more or less abundantly, 

 in most articles generally used as food; and where they are deficient, the ani- 

 mal suffers in consequence, if they are not supplied in any other way. Thus 

 common Salt exists, in no inconsiderable quantity, in the flesh and fluids of 

 animals, in milk, and in the egg : it is not so abundant, however, in plants ; 

 and the deficiency is usually supplied to herbivorous animals by some other 

 means. Thus salt is purposely mingled with the food of domesticated animals ; 



