Elements of agricultural chemistry and geology / [Jas. F.W. Johnston].

  • James Finlay Weir Johnston
Date:
1844
Catalogue details

Licence: Public Domain Mark

Credit: Elements of agricultural chemistry and geology / [Jas. F.W. Johnston]. Source: Wellcome Collection.

    237/248 (page 221)
    —Every one knows that in some animals there is much more fat than in others, but in all a certain portion ex- ists, more or less intermingled with the muscular and other parts of the body. This fat is subject to waste, as the muscles are, and therefore must be restored by the food. All the vegetable substances usually cultivated on our farms contain, as we have seen (p. 190), a not- able quantity of fatty matter, which seems to be intend- ed by nature to replace that which disappears naturally from the body. A full-grown animal, in which the fat may be regard- ed as in a stationary condition, requires no more fat in its food than is necessary to restore the natural loss. In such an animal the quantity of fatty matter found in the excretions is sensibly equal to that which is contained in the food. But to a growing animal, and especially to one which IS fatte7iing, the supply of fatty matter in the food must be greater, than to one in which no increase of fat takes place. It is indeed thought by some, that, in the ab- sence of oil in the food, an animal may convert a portion of the starch of its food into fat,—may become fat while living upon vegetable food in which no large proportion of fatty matter is known to exist. It can hardly he doubt- ed, indeed, I think, that the oi-gans of the living animal are endowed with this ])ower of forming in a case of emergency—that is, when it does not exist ready formed in the food—as much fatty matter as is necessary to oil the machinery, so to speak, of its body. But the'natural source is in the food it eats, and an animal, if inclined to fatten at all, will always do so most readily when it lives upon food in which oil or fat abounds. It docs not however follow, because fat abounds in the food, that the animal should become fatter,—since if starch be deficient in the food, the fat, containing no nitrogen, may be decomiiosed and worked up for the purposes of respiration. This working up of the fat existing in the