The products of combustion pass out by the mouth, just as they would Яy up the chimney of an open fire were the charcoal burned in it. Less food-fuel is required in hot weather than in cold; and less in hot climates than in cold ones. Tropical food contains about twenty to thirty parts in the 100 of charcoal; arctic blubber and fats, from eighty to ninety. The intense cold of the polar regions compels the inhabitants to devour large quantities of food-fuel to keep up the heat of the body to 98°. Arctic travelers state that 20 lbs. of blubber is not an uncommon meal for one person. Dr. Playfair compares the consumption of food in the body to the consumption of fuel in a furnace. "The body," he says, "is the furnace, the food is the fuel, the excrements are the ashes, and the gases respired from the mouth are of the same composition as those which fly up the chimney of the furnace." Of course, burning or consumption, as here spoken of, simply means oxidation; as when we say a metal is burned by rust, it means that the oxygen of the air has combined with the iron, and gradually consumed it. The following is the summing up of Dr. Voelcker as to the two great elasses of food substances: NITROGENOUS COMPOUNDS. Vegetable albumen.-A substance identical in composition with the white of egg. Vegetable fibrin, or gluten.-A compound occurring in considerable quantity in wheat, and giving elasticity to the dough made with wheaten flour. Vegetable caseine.-A substance identical in composition with the curd of milk. Legumin.-A peculiar vegetable principle which derives its name from its occurrence in large quantities in pease, beans, and other leguminous seeds. There are other substances, but in such small proportion or of such rare occurrence as to require no special mention.* NON-NITROGENOUS COMPOUNDS. All oily and fatty matters; starch, or amyline.—Which constitutes the principal part of wheaten flour, oat and barley meal, rice, Indian corn, and the dry matter of potatoes. Sugar.-Which abounds in mangolds, carrots, and turnips. Gum and mucilage.-Constituents of every kind of food. Pectin. The jelly-like substance which is found in carrots, mangolds, turnips, and many other bulbous roots. Cellular and woody fibre.-Substances which constitute chiefly the bulk of straw and hay, and occur abundantly in every other vegetable produce. With these views of the chemistry of the various kinds of food, it has been a matter of no small importance to have analyses of them, showing their constituents, so as to enable any one of them to be valued as a food. It is right to state here that some chemists hold, with Mulder, that vegetable albumen and caseine are not identical. The number of analyses taken of foods has been very great, and in this department the services rendered by Drs. Voelcker and Lankester have been extremely valuable. As in a former division we have given analyses showing the nominal constituents of the cereals, root crops, &c., so now we give analyses showing their nutritive constituents. 16-6 16-6 16.6 16-6 16-6 16.6 16.6 16-6 16.6 16-6 16.6 16.6 16-6 16-6 7-97 96-9 8-15 9-67 6-94 8-57 5-42 8.21 6-56 8-42 90-8 9.03 7-23 6-64 7.50 90-8 16-46 21-63 26-99 20-12 18-88 22-11 22-82 25-87 20-59 20-51 22-66 27-56 19 89 27-24 2-09 3-34 27-62 38-30 33.47 27-76 33-58 39.50 37.88 19-23 15-38 10-63 20-50 11-91 13.96 8-63 3.41 3-11 2-97 3-89 3.65 2-55 37-06 35-35 31-25 30-30 36-55 33-37 32-87 18-79 15-98 13-83 20-27 17-07 15-63 19-68 2-40 2-51 2.30 3.38 OIL-CAKES. Water. Oil.... Flesh-formers.. Head-givers Ash... 66 "In determining the nutritive values of different foods the great points are," says Dr. Anderson, "the albuminous compounds (flesh-formers), and the fats (the heat-producers)." But, important as it is to know this, we are still greatly, nay," continues Dr. Anderson, "altogether in the dark as to the relative value of these two classes of substances." It is easy to know the quantities of each, but the difficulty is to ascertain the nutritive value due to each constituent, when, as is often the case, "two or more of them occur in the same substance." The following table is given by Dr. Anderson as likely to be of some value in determining the value of different foods: PROPORTION OF ALBUMINOUS MATTER CONTAINED IN 100 PARTS. PROPORTION OF OIL CONTAINED IN 100 PARTS OF VARIOUS SUBSTANCES.* * Where the substance, as compared with the above list, is not mentioned, it either contains no oil, or so little that it cannot be accurately determined. |