These are also called the elementary or ultimate principles of organic bodies.

The ashes consist principally of

Nearly all animal products are composed of both organic and inorganic constituents. Some few substances, however, pertain almost entirely to one class: thus, while the enamel of the teeth contains scarcely any organic matter, some of the crystals of uric acid met with in the urine afford scarcely any ash.

In animal tissues or fluids, the ultimate organic elements are combined with one another in a variety of ways, constituting definite compounds, which are known as proximate organic principles: thus in urine we may have all the above-mentioned ultimate principles united with one another, to form the proximate principles, urea, uric acid, sugar, albumen, &c.

The muscular tissue is a very suitable material to be employed for the demonstration of the principal organic and mineral constituents of animal bodies: the same general plan is adopted in other instances.

(153.) ULTIMATE ORGANIC CONSTITUENTS.

a. Desiccation. The flesh or other tissue is cut into small pieces and dried in a water bath until it ceases to lose weight. By this means it is divided into an aqueous portion which has evaporated, and a solid portion which remains. Nearly all animal matters behave in a similar way; but nitrogenous substances having an alkaline reaction, give off water containing a variablę amount of ammonia.

B. Destructive distillation. A few fragments of the dried

flesh are placed in a reduction tube, into the mouth of which are inserted a narrow strip of red litmus paper, and a similar strip of lead paper. On applying the heat of a spirit-lamp, water will condense in the upper part of the tube, proving the presence of oxygen and hydrogen in the flesh-a smell of ammonia will be given off, and the litmus paper become blue, results indicating the presence of nitrogen-the lead paper will become blackened, showing the presence of sulphur-and lastly, a black mass consisting chiefly of carbon will remain in the tube.

y. Incineration. If some of the dried flesh be heated upon a piece of platinum foil, or in a shallow capsule, it will swell up, burn with a smoky flame, and leave an abundant carbonaceous residue. On continuing the application of heat for some time, the carbon will gradually burn away. Its disappearance may be facilitated by occasionally pulverising the coherent residue resulting from the ignition. Throughout the process the temperature should not exceed, or indeed scarcely arrive at, a full red heat. As soon as a pale grey or ochry red ash is produced, the heating may be discontinued.

d. Detection of nitrogen. A little of the finely divided dry substance is intimately mixed with ten or twelve times its bulk of soda-lime (made by slacking quicklime with caustic soda solution) and the mixture heated in a reduction tube, whereby ammonia is given off, recognisable by its smell and reaction on test-paper.

E. Detection of sulphur. Bodies of a moderately light colour may be tested for sulphur by boiling them in aqueous potash, to which solution of acetate of lead has been added in quantity insufficient to render the liquid permanently opaque. Should the substance so treated contain sulphur it will become stained of a brown or black colour, which cannot be removed by subsequent washing with water. If a substance is stained in the above manner when boiled in a potash solution of lead, and is scarcely or not at all deepened in colour when boiled in a solution of pure potash (free from lead), the presence of sulphur is certain.

In the case of bodies readily soluble in potash water, the results are not quite so characteristic.

3. Deflagration with nitre. A little of the dried and finely divided animal matter is mixed with about an equal bulk of powdered nitre, and the mixture projected in small portions at a time into a porcelain crucible kept at a red heat. Deflagration immediately takes place, and, in the fused residue, the presence of carbonic, sulphuric, and phosphoric acids, resulting from the oxidation of carbon, sulphur, and phosphorus respectively, may be ascertained by the usual tests.

In performing the above experiments, very different results will be obtained with different substances, such, for instance, as pieces of flannel, hard white of egg, refined gelatine, sugar, fat, &c.

(154.) ASH OF ANIMAL MATTER.

The re

a. A small portion of the ash, resulting from the incineration of any kind of animal matter, is placed on a watch-glass, moistened with water and examined by test-papers. Should it not have an acid reaction, a drop or so of nitric acid is to be added, and any effervescence due to carbonic acid carefully noted. mainder of the ash is boiled in a small quantity of water for some time, a few drops of carbonate of ammonium solution added, the whole thrown upon a filter, and the filtrate set aside for examination. The residue is then well washed with water, boiled in a little hydrochloric acid with which a few drops of nitric acid have been mixed, the liquid evaporated just to dryness, diluted with water, and filtered. In this manner an aqueous and an acidulous solution are obtained, containing respectively :

B. Treatment of acid solution. A little of this solution may be examined for phosphoric acid by molybdate of ammonium (par. 100 d.), and another portion tested for iron by ferrocyanide or sulphocyanate of potassium (par. 77). To the remainder of the solution acetate of ammonium is added, and, in the event of there being no decided reddening produced, a little perchloride of iron also. The whole is then boiled for some time, whereby a red precipitate of basic phosphate of iron is thrown down, the deposition of which may sometimes be facilitated by the careful addition of ammonia in quantity not sufficient to produce neutrality. The boiling liquid is next filtered, whereby a clear colourless solution should be obtained, perfectly free from both iron and phosphoric acid. Excess of oxalate of ammonium added to this solution throws down a precipitate of oxalate of calcium. The resulting turbid mixture, having been well shaken or stirred, is set aside for a little while, and, after partial subsidence, passed once or twice through filtering paper, when magnesium may be tested for in the clear liquid by means of ammonia and phosphate of ammonium.

7. Treatment of aqueous solution. Separate portions of this solution, acidified with nitric acid, may be tested for sulphates by chloride or nitrate of barium (par. 95 a.); for chlorides, by nitrate of silver (par. 96 a.); and for phosphates, by molybdate of ammonium, or by sulphate of magnesium and ammonia (par. 100 d. a). Or a single portion of the acidified solution may be tested with a few drops of nitrate of barium to precipitate sulphates; then filtered and treated with excess of nitrate of silver to precipitate chlorides; then again filtered and carefully neutralised with dilute ammonia to throw down the yellow phosphate of silver which the previously free nitric acid held in solution.

The remainder of the liquid has to be evaporated to dryness, and the residue, after gentle ignition, dissolved in a small quantity of water. The solution, filtered if necessary, and acidulated with hydrochloric acid, is carefully evaporated down in a watch

glass or capsule, when cubes of common salt will crystallise out, showing the presence of sodium. The mother liquor from these crystals is then to be treated with perchloride of platinum and alcohol, when, on stirring, a crystalline yellow precipitate of platino-chloride of potassium will be deposited. Or the solution, acidified with hydrochloric acid, may be treated at once with perchloride of platinum and alcohol, the yellow liquid filtered from the potassium precipitate and evaporated down, when yellow crystals of platino-chloride of sodium will make their appearance.

§ II.-NORMAL URINE.

(155) GENERAL PROPERTIES.

a. Appearance, &c. Healthy human urine is an aqueous liquid in which various compounds, organic and mineral, are dissolved, and certain other substances held in suspension. It has an amber colour, a slightly acid reaction, a characteristic though not powerful odour, and a sp. gr. usually ranging within a few degrees of 1020. The substances suspended in urine are epithelium and mucus. Its dissolved organic constituents are urea, uric acid, and hippuric acid, with colouring and other extractive matters. Its inorganic or mineral constituents are sodium, potassium, calcium, and magnesium, in the form of phosphates, sulphates, and chlorides. The student is expected to identify these several substances, to make himself acquainted with their characteristic appearances, and to realise their principal reactions. A good quarter-inch object-glass is requisite for microscopic examination.

B. Mucus, epithelium, &c. Recent urine set aside for some little time in a glass vessel gradually deposits a loose flocculent sediment, readily visible upon holding the specimen between the eye and the light. When examined microscopically it is seen to consist of epithelial cells, derived from different portions of the urinary apparatus, together with granular or mucuscorpuscles. By filtration, these suspended urinary constituents