The use of food is to repair the waste daily and hourly going on in our bodies, and to enable us to execute the work for which the body was designed ; also, as we have shown in the first pages of Domestic Science, to keep the lamp of life burning by supporting the animal heat.

To keep a man living and able to work he will require daily five ounces of nitrogenous or flesh-forming food, and ten ounces of calorific matter or carbon, for heat-giving or breathing. Women and schoolboys require two and a half ounces of flesh-formers, and about three-fourths of the man's amount of carbon, or heat-givers.*

"This large quantity of starch or fat is required by a full-grown man daily, in order that he may continue to breathe, and yet retain the weight of his body undiminished.

"That all bodily movement is attended by waste of the bodily substance is a received opinion. But whether such movement is or is not its true cause, the waste itself is certain. An animal when fasting will lose from a fourteenth to a twelfth of its whole weight in twenty-four hours. This loss does not fall altogether upon the fat" - which supplies the animal heat - " but extends also in part to the tissues and general substance of the body. It is so great that the whole blood is unable altogether to replace it. Scarcely, therefore, is the stomach of an animal empty, when it begins already to feed upon itself".

The food required by the body consists of gluten, fibrin, albumen, starch, fat, sugar, and saline matters.

* On the authority of the South Kensington Museum.

Gluten will be readily detected in the dough of bread if it be placed on a sieve and turned about by the hand under a stream of water poured from a jug on it. The water at first passes through milky in appearance ; at last there will remain at the bottom of the sieve a white sticky substance resembling bird-lime. This matter from its glutinous nature has been called "gluten".

If the milky water be allowed to stand, a white powder will sink as a sediment in it, which is wheaten starch.

Gluten contains nitrogen, the kind of air or gas which forms the greater part of the atmosphere. The fibrin of meat, and the albumen or white of an egg, also contain nitrogen nearly in the same proportion as gluten. In these three similar substances, therefore, the nutritive or flesh-forming parts of our food are chiefly found. We must observe here, that albumen in plants is not the same as the albumen which is the white of an egg. It is the white inner part of the seed on which the plants feed, as the chicken does on the albumen in the egg. Albumen, though different in appearance and sensible properties from gluten and fibrin has, as we have just said, a close chemical relation to both and serves nearly the same purpose in feeding animals. Gluten, fibrin, and albumen are all alike nutritive and flesh-forming.

Next in order come the heat-givers, or those substances which by keeping up the internal combustion always going on within, enable us to breathe and live - they are the fats and oils, sugars and starch. Human fat feeds the animal heat in combination with the oxygen of the air. It (human fat) consists of carbon, hydrogen, and oxygen, and is transformed into carbonic acid and water by the oxygen in the air we breathe. This oxygen taken into the blood circulates through our bodies, unites with the carbon and hydrogen of the fat, and changes it into carbonic acid and water, to be breathed off again through the lungs.

Now starch and sugar will take the place of the animal fat, and thus prevent its diminution. They will be breathed away instead of the fat of the animal itself. Ardent spirits, which consist of four parts of carbon, six of hydrogen, and two of oxygen, have the same power of supplying carbonic acid gas for breathing. Starch consists of half its weight in carbon, and hydrogen and oxygen in the proportions which form water - i.e., eight parts of oxygen to one part of hydrogen. It produces when oxidized (that is, united with oxygen) in the system of man, muscular force and animal heat, but it is not either a flesh or muscle former.

Arrowroot, which is a starch, cannot therefore form alone the food of man, who on such a diet would die of slow starvation.

No vegetable production will preserve life unless starch and gluten be united in it.

Wheaten bread will support life, but it lacks fat, required for repairing the waste of animal fat, and to help digestion ; and we consequently eat butter with it. We make tart and pie crusts with butter, lard, or dripping, for the same reason, wheaten flour being deficient in fat; in fact to most vegetables we require to add fat.

Woody fibre will be always found amongst the constituents of vegetable food ; it passes through the animal undigested.

The following table of flesh-formers, each sufficing for the daily food of a man, is given from the Food Gallery of the South Kensington Museum. The various vegetable substances contain the same supply of nitrogen in the varying quantities,

2 lbs. 1oz. of Flour.

2 6 of Barley-meal.

1 13 Oatmeal.*

2 9 Maize.

2 3 of Rye. 4 13 Rice.

3 10 Buckwheat. I 3 of Lentils.

I 5 of dry Peas.

I 5 dry Beans.

2olbs 13oz Potatoes.

31 4 Carrots.

15 10 Parsnips.

17 13 Turnips.

10 6 of Cabbage,

3 13 Bread.

1 11 Tea - dry,

2 1 Coffee - dry, l 8 Cocoa-nibs,

"All parts of the body," says Professor Johnston, "are endowed with the power of selecting from the universally nourishing blood the chemical compounds which are specially required for the formation of their own substance, or the discharge of their special functions. Thus the bones specially select and appropriate phosphate of lime, while the muscles take phosphate of magnesia and phosphate of potash. The cartilages build in soda in preference to potash. The bones and teeth specially extract fluorine. Silica is almost monopolized by the hair, skin, and nails of man.....Iron abounds chiefly in the colouring matter of the blood, in the black pigment of the eye, and in the hair. Sulphur exists largely in the hair, and phosphorus in the brain. Thus to each part of the body certain chemical substances seem to be most specially appropriated, and to each part a peculiar and special power has been given of selecting out of the common storehouse those materials which suit it best to work withal.">

These materials are supplied in our food, and care should be taken by the housewife that bad cooking and injudicious arrangements may not cause the needful substances to be wanting from the food supplied.

We shall now endeavour to guide her judgment in the choice and preservation of food, commencing with a little information respecting the staff of life - our daily bread.

Bread, and the Grains used for making it.

The various kinds of flour used for ordinary English bread are -

Wheat Flour, Oatmeal, Barley-meal, Indian-meal.