486 OF FOOD, AND THE DIGESTIVE PROCESS. 



645. But in regard to the Herbivorous animals, the case is different. They 

 perspire much more abundantly, and their temperature is thus continually kept 

 down. They consequently require a more active combustion, to develope 

 sufficient bodily heat; and the materials for this are supplied, as we have 

 seen, by the non-azotized portions of their food, rather than by the metamor- 

 phosis of their own tissues, which takes place with much less rapidity than in 

 the Carnivorous tribes. Hence we may thus express the destination of this 

 part of their food; that of the azotized matter, here much smaller in amount, 

 will be the same as in the preceding case : 



Starch, oil, and} partly (AT ^ but chiefly C Carbonic acid and Water, dis- 



other non-azotized > converted < > thrown off < engaged by the respiratory 



compounds ) into ( ) directly as ( process. 



The proportion of the food deposited as fat, will depend in part upon the sur- 

 plus which remains, after the necessary supply of materials has been afforded 

 to the respiratory process. Hence, the same quantity of food being taken, the 

 quantity of fat will be increased by causes that check the perspiration, and 

 otherwise prevent the temperature of the body from being lowered, so that 

 there is need of less combustion within the body to keep up its heat. This is 

 consistent with the teachings of experience respecting the fattening of cattle ; 

 for it is well known that this may be 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. 



646. 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 in- 

 habits), 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 ingredients predomi- 

 nate. Thus it has been calculated, that, since fifteen pounds of flesh contain 

 no more carbon than four pounds of starch, a savage with one carcass 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 carcasses, in 

 order to procure the carbon necessary for respiration. Hence we see the im- 

 mense advantage as to economy of food, which a fixed agricultural population 

 possesses over those wandering tribes of hunters, whicli still people a large 

 part both of the old and new continents. The mixture of the nzotized 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 articles of vegetable 

 food, these may be generally estimated by the proportion of azote they con- 

 tain ; which is in almost every instance less than that existing in good wheat 

 flour. 



647. The following table represents the relative quantity of Nitrogen in 

 different articles used as food ; and thus shows their relative applicability to 



