lizing mixed solutions of argol and soda-ash. It is largely used in medicine, forming the chief constituent of Seidlitz powders.

§ 2. Organic Alkaloids.

556. The term alkaloid has been applied to a large number of bodies having the general constitution of amines. They contain carbon, oxygen, hydrogen, and nitrogen, and act as bases. Many compounds analogous to these have been artificially prepared, but the vegetable alkaloids have as yet defied the constructive power of the chemist. They include some of our most violent poisons, and act powerfully on the animal economy. Most of the alkaloids dissolve sparingly in water, but freely in boiling alcohol; are intensely bitter, and usually restore the reddened color of litmus. They are the most powerful medicines and poisons known. Gallotannic acid precipitates most of the organic bases, forming, with them, insoluble compounds; hence it is an excellent antidote. when they have been taken in poisonous doses. We shall notice only the more important alkaloids found in vegetable substances.

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557. Nicotine, C,H,,N,.-This compound is of interest, as the chief alkaloid contained in the smoke of tobacco, and, in fact, is the proximate cause of the narcotic effects produced by the use of that plant, which contains it in quantities varying from two to eight per cent. It is a colorless, transparent oil, which boils at 250° C., giving off very irritating vapors. It is soluble in water, alcohol, and oils. It has a burning taste, even when much diluted, and is one of the most violent poisons known. The effect is said to be produced upon the motor nerves, producing convulsions, and afterward paralysis. Five milligrammes has been found sufficient to kill a medium-sized dog in three minutes.

558. Morphine, C,,H,,O,N.—This is the chief active principle of opium, which is the hardened, milky juice of the

poppy. Opium is a very complex body, containing, besides morphine, a large number of other alkaloids. Morphine (from Morpheus, in consequence of its sleep-inducing property) is a crystallizable, resin-like body, without odor, and possessing a bitter, disagreeable taste. It is a powerful narcotic and poison, and, in the form of the acetate, sulphate, and hydrochlorate, is largely used in medicine. Piperine, CH, NO,, is a substance isomeric with morphine, found in common black and white pepper. It is nearly insoluble in cold water, has an acrid taste, and, when acted upon by nitric acid, develops an odor of bitter-almonds. Capsicine is an alkaloid obtained from Cayenne pepper. It forms crystallizable salts, with acetic, nitric, and sulphuric acids.

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559. Strychnine, C2H2ON,, is chiefly obtained from the beans of the strychnos nux-vomica, a small East India tree, but is found in several other plants belonging to that tribe. Cold water dissolves only of its weight of strychnine, but it is more readily soluble in essential oils and chloroform. From its solutions it crystallizes in small brilliant octahedrons, of exceedingly bitter taste. Such is its intense bitterness, that it imparts it perceptibly to 700,000 times its weight of water. It is a deadly poison, of a grain killing a dog in thirty seconds. It takes effect upon the nerve-centres of the spinal axis, producing fearful convulsions. The terrible woorara poison, with which the South American natives poison their arrows, and which has been lately used as a remedy for tetanus, appears to con tain a principle nearly allied if not identical with strychnine. Bracine is an alkaloid closely allied to strychnine, and obtained from the same genus of plants.

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560. Quinine, C,H2ON,, is extracted from pulverized Peruvian bark by acidulated water. It is a white, crystalline substance, which unites with acids, producing intensely bitter salts. Quinine sulphate, which forms light, bulky crystals, is the salt employed in medicine. It dissolves sparingly in water, but freely in dilute sulphuric acid and

alcohol. Cinchonine is another alkaloid from the same

source.

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561. Caffeine Series.-Two terms of this series are known. Theobromine, C,H,O,N,, is a crystalline alkaloid, obtained from cacao-beans, the source of chocolate. Caffeine or theine, CHON, is an alkaloid, which may be obtained from coffee, tea, and several other plants, the stimulating effects of which are in part due to the presence of caffeine compounds. Coffee seldom contains more than one per cent. of the principle, while tea furnishes three or four. Caffeine crystallizes in long, flexible, silky needles, has a slightly bitter taste, and dissolves sparingly in cold water, but freely in hot water.

The stimulating effects of coffee and tea are, however, not due to the caffeine alone, but are modified by various other ingredients. In tea, the alkaloid is associated principally with tannin and an essential cil; in coffee, with empyreumatic and essential oils.

§3. Albuminous Substances.

562. Under this head are classed a number of compounds, some of which form essential portions of the bodies of animals, and occur in certain parts of vegetables; while others, not properly albuminoids, are obtained, directly or indirectly, from the animal organism. The albuminoids possess constitutions very complicated, and our knowledge of their chemical relations is limited. They do not crystallize, but are found in amorphous, jelly-like form. They contain, in addition to carbon, oxygen, hydrogen, and nitrogen, small quantities of sulphur and phosphorus. Strong mineral acids dissolve all of the albuminoids.

563. Albumen is the chief and characteristic constituent of the serum of the blood, and of white of egg, and occurs in all the fluids which supply nutritive material for the renovation of the animal tissues. It forms about seven

per cent. of blood, and twelve per cent. of the white of egg. Albumen exists in two modifications-the soluble form, and the insoluble variety into which it may be brought by the action of heat, as when white of egg is boiled. These two modifications are identical in chemical composition, and the difference is thought to be due to the presence of certain mineral salts which are associated with the soluble variety. A solution of albumen, heated to 72° C., is coagulated.

Vegetable albumer abounds in the juice of many soft, succulent plants used for food; it may be extracted from potatoes by macerating the sliced tubers in cold water containing a little sulphuric acid.

564. Musculine is the name given to the substance which forms the basis of muscular tissue.

FIG. 200.

This occurs in

bundles, as shown in Fig. 200, the parallel fibres having wrinkles or cross-markings. If a piece of lean beef be washed in clean water, its red color, which is due to blood, gradually disappears, leaving a whitish mass composed of musculine, and the areolar tissue which binds the fibres of the muscle together. Like albumen, it is capable of being converted into an insoluble body. Fibrine is a constituent of blood, forming in the healthy state about two parts in 1,000 parts of that liquid. The clotting of blood, when freshly drawn, is due to the coagulation of its fibrine, which solidifies into a net-work of fibres. Dilute solutions of potash and soda dissolve fibrine, as they do albumen. When wheat-flour is made into dough, and then kneaded on a sieve, or a piece of muslin under a stream of water, its starch is washed away, and there remains a gray, tough, elastic substance, almost resembling animal skin in appear

ance.

When dried it has a glue-like aspect, and is therefore called gluten. The crude gluten thus prepared, when freed from oil, albumen, etc., proves to be identical with animal albumen.

The effect of boiling upon fibrine is to render it hard and tough. Heat, as we have seen, converts soluble into coagulated albumen which is insoluble in water, either hot or cold.

565. Caseine is an essential constituent of milk, existing in it to the extent of about three per cent., and forming its curd, or cheesy principle. In milk it is held in solution by the presence of a small portion of free alkali, and, when this is neutralized by an acid, the caseine is precipitated, or the milk curdles. By neutralizing the acid, the caseine is redissolved. Almonds, peas, beans, and many other seeds, contain an albuminoid closely resembling caseine, sometimes known as legumine, or vegetable caseine. This is not coagulable by heat, but by alcohol and acetic acid. The coagulated legumine resembles the curd of milk. The Chinese make a cheese from peas, which gradually acquires the smell and taste of milk-cheese.

Milk is a secretion of special interest from the circumstance that it constitutes the entire food of the young animal for some months, and consequently must contain all the elements necessary for the rapid development of the various tissues of the body. It has essentially the same constituents in carnivorous animals that it has in the herbivorous, although the proportions are somewhat variable. When examined under a microscope it is seen to consist of a transparent fluid, in which float transparent globules consisting of fat, surrounded by an envelope of albumen. When milk is allowed to remain at rest for a few hours, at the ordinary temperature of the air, the fat-globules rise to the surface; and, if the layer of cream thus formed be removed and subjected to mechanical action, the albuminous envelope is broken, and the globules of fat coalesce