For respiration. For waste of muscle, &c. 1¾ lbs. of bread yielding 18 oz. starch and 3 oz. of gluten. 8 oz. of beef yielding 2 oz. of fibrin. Total consumed by respiration,} } gluten or and the ordinary waste, } 18 oz. starch and 5 oz.} fibrin. If, again, the 7½ lbs. of potatoes be eaten, then in these are contained about 2½ ounces of gluten or albumen, so that there remain 2½ ounces to be supplied by beef, eggs, milk, or cheese. The reader, therefore, will understand why a diet which will keep up the human strength is easiest compounded of a mixture of vegetable and animal food. It is not merely that such a mixture is more agreeable to the palate, or even that it is absolutely necessary,—for, as already observed, the strength may be fully maintained by vegetable food alone;—it is, that without animal food in one form or another, so large a bulk of vegetable food must be consumed in order to supply the requisite quantity of nitrogen in the form of gluten. Of ordinary wheaten bread alone, about 3 lbs. daily must be eaten to supply the nitrogen,[24] and there would then be a considerable waste of carbon in the form of starch, by which the stomach would be overloaded, and which, not being worked up by respiration, would pass off in the excretions. The wants of the body would be equally supplied, and with more ease, by 1¾ lbs. of bread and 4 ounces of cheese. [24] The flour being supposed to contain 15 per cent. of dry gluten, on which supposition all the above calculations are made. Of rice, again, no less than 4 lbs. daily would be required to impart to the system the required proportion of gluten; and it is a familiar observation of those who have been in India and other countries, where rice is the usual food of the people, that the degree to which the natives distend, and apparently overload their stomachs with this grain, is quite extraordinary. The stomachs and other digestive apparatus of our domestic animals are of larger dimensions, and they are able, therefore, to contain with ease as much vegetable food, of almost any wholesome variety, as will supply them with the quantity of nitrogen they may require. Yet every feeder of stock knows that the addition of a small portion of oil-cake, a substance rich in nitrogen, will not only fatten an animal more speedily, but will also save a large _bulk_ of other kinds of food. 3. But the blood and other fluids of the body contain much _saline_ matter of various kinds, sulphates, muriates, phosphates, and other saline compounds of potash, soda, lime, and magnesia. All these have their special functions to perform in the animal economy, and of each of them an undetermined quantity daily escapes from the body in the perspiration, in the urine, or in the solid excretions. This quantity, therefore, must be daily restored by the food.