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862

CARTILAGE-WHITE FIBROUS AND MUSCULAR TISSUES.

monium acetate; boiling concentrated solution of potash does not affect it. This substance is one of the simplest forms of the nitrogenised plastic materials. It presents some points of analogy with vegetable fibre, particularly in the production of acetic acid by its decomposition.

The compound to which Fremy assigns a composition isomeric with that of cellulin is distinct from chitin. Berthelot calls it tunicin (1106), from its entering into the composition of the envelope of some of the tunicate mollusks. It yields, when treated with

acids, products similar to those furnished by chitin.

(1673) Cartilage. The articular extremities of the bones are encrusted with a white elastic opaque horny substance which contains but little saline admixture (from 3 to 6 per cent. of salts); by long boiling it is gradually dissolved, and forms a liquid which on cooling furnishes a tremulous jelly. The transparent cornea, the rings of the trachea, the elastic parts of the ears, nose, and eyelids, and the flexible prolongations of the ribs are also composed of the same material; this substance, however, is not true gelatin, but the modification of it termed chondrin (1662).

White fibrous tissue, and the material of which the tendons, ligaments, and inelastic tendinous expansions are composed, consist of a substance which by continued boiling is almost completely dissolved, and a solution of gelatin is formed, which gelatinizes on cooling. Yellow fibrous tissue has a different composition it is insoluble in boiling water, and in weak acids and alkalies, but is readily soluble in hot concentrated sulphuric acid, and in a strong solution of potash. It resists putrefaction for a long time, and possesses great elasticity. Nitric acid forms a yellow compound with it. The yellow fibrous tissue is an advantageous source of leucine when digested with sulphuric acid which has been diluted with 1 parts of water.

(1674) Muscular tissue consists principally of fibrin in a coagulated form, but being highly vascular, and containing nearly three-fourths of its weight of water, it is permeated with a fluid consisting partly of blood and partly of substances secreted from it, independently of a small proportion of nervous and adipose matter. If lean beef be minced fine, and digested in three-fourths of its weight of cold water and then expressed, this treatment being repeated twice, a solution will be obtained which contains in a concentrated form the soluble constituents of the muscular tissue. These consist chiefly of albumin, the soluble salts of the

JUICE OF FLESH-INOSIC ACID.

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blood, of the crystallizable animal principles termed kreatine and inosin, of phosphoric acid, and at least three organic acids, viz., the lactic, the inosic,* and the butyric; possibly also acetic and formic acids are present in small quantity; the colour of the solution is due to the red colouring matter of the blood. The salts consist chiefly of potassic and magnesic phosphates, and a small quantity of sodic chloride, and of calcic phosphate.

When this expressed liquid is heated nearly to the boiling point, the albumin becomes coagulated, carrying with it a large proportion of the colouring matter; this coagulum generally amounts to between 2 and 3 per cent. of the fresh muscle operated on.†

(1675) Inosic Acid (H2€10H12N411? Liebig).--This compound derives its name from ivòs, of fibre.' It presents the appearance of a syrupy liquid, which is not soluble in alcohol. It has an agreeable taste of the juice of meat, and becomes readily decomposed, mere boiling of the solution producing its partial decomposition.

Inosic acid may be prepared from the mother-liquor obtained from the flesh of the common fowl after the separation of the kreatine (1607): alcohol is to be added to this liquid till it becomes milky, when it is set aside to crystallize, and the baric and potassic inosates are slowly deposited; they are dissolved in water, and baric chloride is added to the hot aqueous solution; on cooling, the baric inosate crystallizes; by a second crystallization this salt is obtained in a state of purity, and the acid may be obtained from it by the cautious addition of sulphuric acid.

The salts which inosic acid forms with the alkalies may be crystallized. When decomposed by heat, they emit an agreeable smell of roast meat. Potassic inosate crystallizes in long delicate four-sided prisms, which are sparingly soluble in alcohol. Baric inosate crystallizes in scales of a pearly lustre, which effloresce in a dry air; they are sparingly soluble in cold water, but freely so in boiling water, and are insoluble in alcohol. Cupric inosate forms a light blue insoluble powder which is not dissolved by acetic acid.

(1676) Inosin, Inosite, or Muscle Sugar (H12, 2 H2O).— This interesting body was discovered by Scherer in the juice of

* This acid, according to Gregory, is found only in the flesh of the common fowl and of the turkey.

+ The juice of flesh, when carefully freed from fat and concentrated by evaporation, is now prepared in large quantities in countries where cattle are abundant, and is sold as Liebig's extract of meat.

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INOSIN.

flesh but according to Lehmann it is only found in the involuntary muscles, the heart yielding it most readily; it has been found in the urine in Bright's disease (Cloetta), and in the same secretion in diabetes (Hohl). It may be obtained by the following process:-After separating the kreatine by crystallization, the baryta is removed by the cautious addition of sulphuric acid so long as it occasions a precipitate. The liquid is then filtered, and the free lactic acid separated by repeatedly washing with ether. Alcohol is added to separate the salts; and by gradually increasing the quantity of alcohol, small crystals, resembling those of gypsum, are formed; these crystals consist of inosin. They must be redissolved in water, and recrystallized. Inosin has recently been shown by Vohl to be identical with phasco-mannite, which is obtained from the seed of the common kidney-bean, Phaseolus vulgaris.

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Inosin forms colourless efflorescent prisms, which at a temperature somewhat below 212° lose nearly 17 per cent., or 2 atoms of water. The residue has then the composition of grapesugar which has been dried at 212°. At 410° the dry mass melts to a colourless liquid, which, on cooling, quickly sets into a crystalline mass. It has a sweet taste, and is freely soluble in water, less so in rectified spirit, and is insoluble in absolute alcohol and in ether. Dilute acids and alkalies, even when boiled with it, produce no change. Its solution has no rotatory action upon a ray of polarized light. With concentrated nitric acid it yields a nitro-substitution compound (ЄH(NO2),→。), and this may be precipitated in oily drops, which crystallize, by the addition of concentrated sulphuric acid. Nitro-inosin is freely soluble in alcohol, but not in water, and explodes when sharply struck. It may be obtained crystallized in colourless rhombohedra. A solution of inosin to which caustic potash has been added dissolves hydrated cupric oxide with a blue colour, but does not reduce it to cupreous oxide when the liquid is boiled. The solution of inosin gives a white precipitate when mixed with one of basic acetate of lead. Inosin is not susceptible of the vinous fermentation, but with chalk and cheese it yields lactic and butyric acids.

(1677) Chemical Effects of Cooking upon Food.-A consideration of the chemical constituents of muscular tissue enables us readily to understand the principal changes produced in the cooking of meat. The common processes of cooking have been very clearly explained by Liebig.

The operation of roasting consists in the gradual coagulation

CHEMICAL EFFECTS OF COOKING UPON FOOD.

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of the albumin, as the heat penetrates from the surface towards the interior: those parts which are nearest the centre, unless the roasting be continued for a sufficient length of time, do not become hot enough to allow the albumin to coagulate; hence they appear red, juicy, and underdone as it is called; the superficial portions become brown, and partially altered in composition, but the greater part of the sapid and saline constituents of the juices contained in the meat are retained, although a certain proportion exudes, and a part of the fat is melted off, and collects below, as dripping.

In boiling meat the result is somewhat different: when the flesh is placed in cold water, and the heat is gradually raised, the soluble albumin, the soluble salts, and the flavouring portions of the meat (which are contained entirely in the soluble parts), begin to pass out into the water, and the meat gradually becomes impoverished, while the liquid in which it is boiled gains in a corresponding degree in flavour and nutritive qualities-the meat becoming hard, ragged, fibrous, and tasteless at the surface, owing to the loss of its albuminous cement. When the water boils, the heat gradually penetrates the mass of the flesh, and as soon as it has risen high enough to coagulate the albumin which is still left in the central portions, the joint is said to be cooked through.

In order to preserve the full flavour of the meat during the boiling, it is necessary to make the water boil before introducing the joint to be cooked, and then to maintain it gently simmering until every part of the mass has attained a temperature of at least 170° or 180°. By this treatment, the albumin contained in the superficial layer of the meat is suddenly coagulated, and thus offers an obstacle to the free escape of the soluble portions from within; the meat therefore is proportionately richer, whilst the broth suffers to the same extent.

Liebig has introduced an improved method of preparing strong meat tea for invalids, founded upon the foregoing considerations. Lean beef or other meat is minced finely while raw, mixed with an equal weight of cold water, and slowly heated to boiling.' After boiling for a minute to coagulate the albumin, the liquid is strained through a cloth, and the fibrous portion exposed to pressure; the broth thus obtained is seasoned with the usual condiments, and furnishes a nutritive soup of excellent flavour, which would gain nothing by longer boiling, but it has little colour.

A still more nutritious broth may be obtained in the following manner: Take one-third of a pound of raw beef or chicken,

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COMPONENTS OF THE BRAIN.

mince it very finely, and mix it with 14 ounces of cold distilled water, to which four drops of hydrochloric acid and from 10 to 18 grains of salt have been added; digest for an hour, and strain out the meat upon a hair sieve; wash the residue upon the sieve with 5 ounces of distilled water. In this way about a pint of a cold extract of meat is obtained, which may be taken cold, or if warm, it must not be heated above 120° (50° C.). The whole of the uncoagulated albumin, one of the most nutritive constituents of the meat, is thus extracted and administered to the invalid; whereas, if the broth be boiled, the albumin becomes coagulated, and is skimmed off and wasted.

The undissolved fibrin when washed once or twice becomes hard and insipid, and is difficult of digestion. The dark colour of soup contributes scarcely anything to its flavour, but custom leads us to associate the idea of strength and flavour with its appearance. The brown tint which long boiling gives, may, as is well known in the kitchen, be supplied by a little burnt sugar, and thus the eye as well as the palate may be satisfied.

The antiseptic power of common salt in preserving meat has been known from time immemorial, but no satisfactory explanation of its mode of action has been given. The process of salting detracts considerably from the nutritive value of the flesh so preserved. When raw meat is salted, the liquid portion speedily begins to ooze out, and to dissolve the salt, forming what is commonly termed brine, which is a saturated solution of salt in the juice of the flesh; the meat thus becomes proportionately impoverished of its albumin and of its sapid and saline components, and at the same time is deprived of its tendency to putrefy.

(1678) Components of the Brain.-The chemical knowledge of the components of the brain and nervous system is less satisfactory than that of many of the foregoing substances. It may be observed that these organs are especially remarkable in a chemical point of view. Fremy, a few years ago, published an investigation upon their composition, which has since been confirmed by Von Bibra in its essential points. The brain contains a large proportion of albumin in the uncoagulated form; but it seems to owe its peculiar properties to the presence of a solid fatty acid, termed cerebric acid, from cerebrum, the brain; this acid contains phosphorus. The brain also contains another phosphorized but oily acid, called oleophosphoric acid. In addition to these bodies, cholesterin, myelin, and the ordinary fats, stearin and olein, are likewise present.

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