either single or few equivalent numbers. They are mostly crystallizable. Our knowledge of these substances is not exact, as incineration, by which they are obtained, expels the volatile bodies, and oxidizes many others. They may be subdivided into-1. Those that are mechanically useful; 2. Those that are chemically useful; and, 3. Those that are accidental, and of no apparent use.

1. Water (HO) is essentially necessary to maintain, by its solvent power, all the great functions of the body, and to it are due most of the physical properties of the tissues, such as pliancy or elasticity. Its evaporation also duly cools the surface. It forms more than twothirds of the weight of the body, constituting in 1,000 parts, of epidermis 37, teeth 100, bones 133, muscle 750, brain 789-the vital endowment of any tissue appearing to be proportional to its amount of water. Blumenbach had a mummy which weighed but 71lb. About 4lb. of water are daily ingested as food or drink, and egested as urine, sweat, pulmonary and alvine discharges, the amount of each excretion being often vicarious.

Phosphate of Lime (8 Ca O, 3 PO, ), of which there are 5 or 61b in the body, confers hardness on nearly all the tissues. Enamel, which is so hard as to strike fire with steel, contains 885, bone 550, muscle 2.5, blood 0.3. It is kept dissolved by the alkaline albumen in the blood, and by biphosphate of soda in the urine. Lactic acid also will take up more than one-half its bulk of this salt. Rickets during dentition, and ununited fracture during pregnancy, are explained by the teeth and fœtus appropriating so much of this mechanically useful salt, which has also been found nearly absent in osteo-malakia.

Carbonate of Lime (Ca O, CO2 ) is found in the skeleton (especially in that of invertebrates and in bony growths). It may be amorphous, as in bones; or dissolved in carbonic acid; crystalline, as in the earconcretions. It is said to be absent in osteo-malakia.

Phosphate of Magnesia (2 Mg O, PO5) usually accompanies phosphate of lime, which it exceeds in fæces, being introduced in the cereal grains. In typhus, the phosphate of ammonia and magnesia has been found adherent to the Peyerian patches.

Fluoride of Calcium (Ca Fl) was discovered in teeth and bones by Von Bibra, especially those that are fossil. Liebig found it in bones from Pompeii, and it exists in blood, milk, &c. Silica often occurs (perhaps accidentally) in blood, bile, and urine,

2. Chloride of Sodium (Na Cl) is the most important of the substances which are chemically useful, and is found in all the tissues, save enamel-vitreous humour 14, cartilage 11, blood 4.5, bile 3.5, urine 3, bone 2.5, and muscle 2. There are about 4 ounces in the entire body. It is introduced in the separate state with the food of all people, excepting the South Sea Islanders and some South Americans, who, however, live on a salt-water fish diet. Most aliments contain it, except perhaps muscle juice and yolk of egg-hence their insipid taste. Its uses are, to increase solubility of albumen, to prevent coagulation of the blood, to furnish hydrochloric acid for the gastric juice and soda for the bile, to aid in carrying the urea from muscle, and, lastly, is useful in the process of osmose by altering the specific gravity of the fluids. It is excreted by the urine, save in pneumonia, when it accumulates in the lung. Cattle require this substance, for, when denied it, they lose condition. One-fifth less is excreted than is introduced as food, probably being decomposed into chloride of potassium and phosphate of soda.

Carbonate of Soda (Na O, CO2) occurs in the blood, keeping the albumen fluid, neutralizing acids, which may be formed in the body, and promoting the oxidation of organic bodies, especially sugar. It is obtained from the tartrates, citrates, and mulates in vegetable food, the organic acid being changed into carbonic acid.

The Alkaline Phosphates are found in such tissues

where common salt is deficient, as blood cells, muscle, and yolk of egg. They render more soluble the earthy phosphates. They are contained in cereal grains. The want of these potash salts produces scurvy, and limejuice, which Sir G. Blane showed was prophylactic, contains citrate of potash plentifully. The potash salts abound in muscle and blood-cells, the soda in blood

serum.

Sulphur is found in the protein bodies, the cuticle and its appendages, and most largely in the taurin of the bile and the cystin of the urine. It occurs in the sulphates in urine, and in the sulpho-cyanide of potassium in saliva.

Phosphorus is contained in all the protein bodies, in nervous matter, and as phosphates in all the tissues. Liebig denies that any uncombined phosphorus exists.

Iron is found in the free state in the blood, as a chloride in gastric juice, and a phosphate in the spleen. It is abundant in colouring matter, as that of bile, hair, &c. Iron is contained in such quantity that the French are said, after burning the body, to have made a mourning ring out of it. A small commemorative medal might be also struck.

3. Among those bodies which are accidental, are manganese, which accompanies iron in blood, hair, &c., especially, it is said, in Scotchmen, who use so much oats as food-that grain containing it rather abundantly. It exists also in the lettuce, asparagus, cauliflower, and other vegetables. Orfila believed that arsenic was a normal constituent, but it merely appears if introduced as medicine, when, being cumulative, it remains for some time in the liver. The same may be said of lead and copper, but the latter is constant in the livers of some molluscs and crustaceans. Iodine is said to escape in the human breath, except in the Genevese, who are so subject to goître.

II. The Unnitrogenized Group are of more complex nature. They are mainly derived from the vegetable kingdom, many of them crystallize, and all consist of carbon, hydrogen, and oxygen.

Starch occurs in the ventricles and grey substance of the brain, and in special-sense nerves, according to Virchow, but is probably a pathological product. It is ingested in great quantities in bread and vegetables; arrow-root, sago, salep from the orchids, and Irish moss, are nearly pure starch. In powder it may be known by crackling between the fingers; it is arranged in granules either single, as in the potato, or grouped in a capsule of cellulose, which substance escapes undigested. Starch diffuses, but does not dissolve in cold water, but hot water bursts its capsules, producing a gelatinous mass, which dries into an insoluble crust. Its solution gives the wellknown blue colour with iodine. Starch itself is useless as food, but by taking two equivalents of water becomes sugar (C12 H10 O10+2 HO=C12 H12 O12). This conversion occurs in seeds when germinating, or malting, in food by fermentation excited by salivin, or on boiling with dilute acid, by which the intermediate substances, gum and dextrin, are produced.

The Sugars are very soluble in water, from which they crystallize; by fermentation they yield carbonic acid and alcohol. Their general formula is C12 H12 O12, and the following varieties only differ in the amount of water they contain:-Glycose, or grape sugar (C12 H12 O12+2 HO), lactose or milk sugar (C12 H12 O12), hepatose or liver-sugar (C12 H12 O12 + 2 HO), inosite or muscle-sugar (C12 H12 012 +4 HO). Sucrose, or canesugar, and some others, do not occur in animal bodies. Sugar may be recognised by the following tests. Moore'sAdd liquor potassæ; boil, and the fluid becomes a brownish red. Heller further states that a few drops of nitric acid develops the odour of burnt sugar. Trommer's-Add liquor potassæ, and then gradually a weak

solution of sulphate of copper; at once a blue colour or slight blue precipitate is formed; boil for a few minutes, and the fluid becomes orange, and at last deposits an ochre-brown suboxide of copper, the sugar having abstracted oxygen from the sulphate of peroxide of copper. Dalton states that the organic constituents of urine, gastric juice, &c., interfere with this test by preventing the precipitation of the suboxide. They can be removed by filtering with charcoal. Maumene's-Soak white woollen cloth in solution of chloride of tin; when dry, dip it in the fluid to be tested, and heat it to 212° (as before the fire), and if sugar be present, a shining black spot will appear. Starch, however, gives the same appearance. Fermentation also indicates the presence of sugar. Add some pure yeast to the fluid in a test-tube inverted, and after a few hours carbonic acid is evolved; if a mercury bath be used, its amount in the top of tube affords a rough quantitative estimate. Alcohol is also formed, and the microscope shows the torula cerevisiae, or yeast plant.

Sugar is found in the blood, especially that of the hepatic vein and the right side of the heart, in milk, in the liver abundantly, and in the urine in diabetes mellitus, as will be noticed hereafter. Inosite is a sugar discovered by Scherer in the muscular tissue of the heart, but as yet it has no physiological interest.

The Fats are the last unnitrogenized group we shall describe. They are composed of carbon, hydrogen, and oxygen in varying proportions, and these elements are arranged as a fatty acid and the base glycerin, or, according to some chemists, the oxide of lipyl. If the acid and base be separated, fat is not again formed by their mixture. Glycerin is a sweet, limpid fluid, which is separated when any other base (as oxide of lead in the making of litharge plaster) unites with the fatty acid. As it does not evaporate, it has been found most useful in pharmacy and medicine. Brain and yolk of egg are