It is solid; pulverulent; when dry, insipid, inodorous, and heavier than water. When decomposed by heat, it yields carbonate of ammonia, charcoal, &c. It is insoluble in water, alcohol, and the oils; but soluble in alkalies. On the gradual addition of nitric acid to a fluid, which contains this substance in solution, a very characteristic series of tints is evolved. The fluid becomes first blue, then green, afterwards violet and red, and ultimately assumes a yellow or yellowish-brown colour. On adding an acid to a solution of biliphain, a precipitation of green flocculi takes place: these possess all the properties of chlorophyll, or the green colouring matter of leaves. In this state it is termed biliverdin by Berzelius; and is a product of the metamorphosis of biliphin.

1

These are the chief nitrogenized organic elements.

b. Organic Elements that do not contain Nitrogen.

1. Olein and Stearin.-Fixed oils and fats are not pure proximate principles, as was at one time supposed. They were long presumed to consist of two substances, one of which is solid at the ordinary temperature of the atmosphere, and the other fluid: the former of these was called Stearin, from orsap, suet; the latter Elain or Olein, from #λator, oil. Stearin is the chief ingredient of vegetable and animal suet; of fat and butter; and is found, although in small quantity, in fixed oils. In suety bodies, it is the cause of their solidity. Elain and stearin may be separated from each other by exposing fixed oil to a low temperature; and pressing it, when congealed, between folds of bibulous paper. The stearin is thus obtained in a separate form; and by pressing the bibulous paper under water, an oily matter is procured, which is elain in a state of purity. Modern chemistry has shown, however, that fat contained in the cells of adipose tissue is composed of a base termed glycerin-itself hydrated oxide of glyceryl-with stearic and margaric acids. Stearin is a bi-stearate of glycerin:olein, or elain, an oleate of glycerin.

2. Fatty matter of the Brain and Nerves.-Vauquelin' found two varieties of fatty matter in the brain,-the one white, the other red, the properties of which have not been fully investigated. Both give rise to phosphoric acid by calcination, without there being any evidence of an acid, or phosphate in their composition. They may be obtained by repeatedly boiling the cerebral substance in alcohol; filtering each time; mixing the various liquors, and suffering them to cool:-a lamellated substance is deposited, which is the white fatty matter. By evaporating the alcohol, which still contains red fatty matter and osmazome, to the consistence of bouillie; and exposing this, when cold, to the action of alcohol, the osmazome is entirely dissolved, whilst the alcohol takes up scarcely any red fatty matter.

3. Acetic acid. This acid exists in a very sensible manner in sweat, urine, and milk-even when entirely sweet. It, or lactic acid, is formed in the stomach in indigestion; was found by the author and his late friend, Professor Emmet, contained in the gastric secretions in health,

1

Simon, op. cit., p. 44.

"Annales de Chim., lxxxi. 37.

and is one of the constant products of the putrid fermentation of animal or vegetable substances. It is the most prevalent of the vegetable acids, and most easily formed artificially.

4. Oxalic acid.-This acid,-which exists extensively in the vegetable kingdom, but always united with lime, potassa, soda, or oxide of iron,-is only found, combined with lime, as an animal constituent in certain urinary calculi.

5. Benzoic acid.-This acid, found in many individuals of the vegetable kingdom, is likewise met with in the urine of the horse, cow, camel, and rhinoceros; and sometimes in that of man, especially of children. When benzoic acid is swallowed, hippuric acid is observed in the urine; and it was supposed by Mr. A. Ure and others, that this was owing to the conversion of uric acid into hippuric; and as the hippurates are more soluble, it was suggested by him, that benzoic acid might be advantageously exhibited in lithuria, and in cases of gouty depositions of lithate of soda. It has been found, however, by Drs. Keller and Garrod,' and by Professor Booth, and Mr. Boyé, of Philadelphia, that the administration of benzoic acid exerts no influence on the amount of uric acid in the urine.

6. Lactic acid.-Acid of milk is met with in blood, gastric juice, urine, milk, marrow, and also in muscular flesh. At times it is in a free state, but is usually united with alkalies. However much it may be concentrated, it does not crystallize, but remains under the form of syrup or extract. When cold it is tasteless, but when heated has a sharp acid taste. According to Dr. Prout, this acid, like urea, results from the decomposition of the gelatinous parts of the system; according to Berzelius, however, it is a general product of the spontaneous decomposition of animal matters within the body. Liebig3 formerly denied, that any lactic acid is formed in the stomach in health; and affirmed, that the property possessed by many substances, such as starch, and the varieties of sugar, by contact with animal matters in a state of decomposition, of passing into lactic acid, had induced physiologists too hastily to assume the fact of the production of lactic acid during healthy digestion:-yet he now admits its presence.

7. Sugar of milk. This substance, which is so called because it has a saccharine taste, and exists chiefly, if not solely, in milk, differs from ordinary sugar in not fermenting. It is obtained by evaporating whey, formed during the making of cheese, to the consistence of honey; allowing the mass to cool; dissolving; clarifying and crystallizing. It commonly crystallizes in regular parallelopipedons, terminated by pyramids with four faces. It is white; semitransparent; hard, and of a slightly saccharine taste.

8. Sugar of diabetes.-In diabetes mellitus, the urine, which is often passed in enormous quantity, contains, at the expense of the economy, a large amount of peculiar saccharine matter, which, when properly purified, appears identical in properties and composition with vegetable

'Liebig's Animal Chemistry, p. 316.

'Proceedings of the American Philosophical Society at the Centennial Celebration in Phila., May, 1843, and Transactions of the A. P. Society, vol. ix. pt. 2, Philad., 1845.

3 Op. cit., p. 107.

sugar, and approaches nearer to the sugar of grapes-glucose-than to that of the cane. It is obtained in an irregularly crystalline mass, by evaporating diabetic urine to the consistence of syrup, and keeping it in a warm place for several days. It is purified by washing in cold, or-at the most-gently heated alcohol, till the liquor comes off colourless; and then dissolving it in hot alcohol. By repeated crystallization it is thus rendered pure. In the notes of two cases of diabetes mellitus now before the author, it appears, that sixteen ounces of the urine of one patient, of the specific gravity of 1.034, afforded a straw-coloured extract, which, when cold and consolidated, weighed one ounce and five drachms. The same quantity of the urine of the other patient, specific gravity 1.040, yielded one ounce and seven drachms. Neither extract appeared to contain urea when nitric acid was added; but when a portion was dissolved in water, and subjected to a temperature of 2120, traces of ammonia were manifested on the vapour being presented to the fumes of chlorohydric acid. From this a conclusion was drawn, that urea was present, as it is the only known animal matter decomposed by the heat of boiling water. In a little more than a month, the subject of the latter case passed about four hundred and eighty pints of urine, or about seventy-five pounds troy of diabetic sugar!

9. Bilin or Picromel.-M. Thénard2 discovered this principle in the bile of the ox, sheep, dog, cat, and several birds; Chevalier, in that of man. To obtain it, the acetate of lead of commerce must be added to bile until there is no longer any precipitate. By this means, the yellow matter of the bile and the whole of the fatty matter are thrown down, united with the oxide of lead; the phosphoric acid of the phosphate of soda, and the sulphuric acid of the sulphate of soda, are likewise precipitated. The picromel may then be thrown down from the filtered liquor by the subacetate of lead. The precipitate, which is a combination of picromel with oxide of lead, must now be washed and dissolved in acetic acid. Through this solution, sulphuretted hydrogen is passed to separate the lead; the solution is then filtered, and the acetic acid driven off by evaporation.

Pure picromel is devoid of colour, and has the same appearance and consistence as thick turpentine. Its taste is at first acrid and bitter, but afterwards sweet. Its smell is nauseous, and specific gravity greater than that of water. When digested with resin of bile, a portion of the latter is dissolved, and a solution obtained, which has a bitter and a sweet taste, and yields a precipitate with the subacetate of lead and the stronger acids. This is the compound that causes the peculiar taste

of the bile.

10. Cholesterin. This is a constituent principle of the blood, bile, medullary neurine, and vernix caseosa. It is often precipitated from bile in a crystalline state; and forms of itself concretions which have an evidently laminated texture. It has been very frequently met with in morbid secretions and tissues; in the fluid of dropsies; in that of cysts and hydatids; and in medullary fungus and other tumours. At

Prout, Medico Chirurg. Transact., viii. 538.

" Mémoir. d'Arcueil, i. 23, and Traité de Chimie, tom. iii.

times, it is dissolved; at others, swims upon the fluid in brilliant plates, or forms solid masses. It is obtained from biliary calculi by boiling in water, and dissolving them afterwards in boiling alcohol. On cooling, crystals of cholesterin separate.

These inorganic and organic elements-with others of less moment discovered by modern chemists-variously combined and modified by the vital force, constitute the different parts of the animal fabric. Chemistry, in its present improved condition, enables us to separate them, and to investigate their properties; but all the information we derive from this source relates to bodies, that have been influenced by the vital force, but are no longer so; and in the constant mutations that occur in the system whilst life exists, and under its controlling agency, the same textures might exhibit very different chemical characteristics, could our researches be directed to them under those circumstances. Whenever, therefore, the physiologist has to apply chemical elucidations to operations of the living machine, he must recollect, that all his analogies are drawn from dead matter, which differs so widely from the living as to suggest the necessity of a wise and discriminating caution.

The components of the animal body are invariably found under two forms-solids and fluids. Both are met with in every animal, the former being derived from the latter; for, from the blood every part of the body is separated; yet they are mutually dependent, for every liquid is contained in a solid. The blood itself circulates in solid vessels. Both, too, possess an analogous composition; are in constant motion, and incessantly converted from one into the other. Every animal consists of a union of the two; and this union is indispensable to life. Yet certain vague notions with regard to their relative preponderance in the economy, and to their agency in the production of disease, have led to discordant doctrines of pathology,—the solidists believing, that the cause of most affections is resident in the solids; the humorists, that we are to look for it in the fluids. In this, as in similar cases, the mean will lead to the most satisfactory result. The causes of disease ought not to be sought in the one or the other exclusively.

c. Of the Solid Parts of the Human Body.

A solid is a body whose particles adhere to each other, so that they do not separate by their own weight; but require the agency of some extraneous force to effect the disjunction. Anatomists reduce all the solids of the human body to twelve varieties;-bone, cartilage, muscle, ligament, vessel, nerve, ganglion, follicle, gland, membrane, areolar membrane, and viscus.

1. Bone is the hardest of the solids. It forms the skeleton; the levers for the various muscles to act upon; and serves for the protection of important organs.

2. Cartilage is of a white colour, formed of very elastic tissue; covering the articular extremities of bone to facilitate their movements; sometimes added to bones to prolong them, as in the case of the ribs;

at others, placed within the articulations to act as elastic cushions; and, in the fœtus, forming a substitute for bone. Hence, cartilages are divided into articular or incrusting, cartilages of prolongation, interarticular cartilages, and cartilages of ossification.

3. Muscles constitute the flesh of animals. They consist of fasciculi of red and contractile fibres, extending generally from one bone to another; and are the agents of all movements.

4. Ligaments are tough; difficult to tear; and, under the form of cords or membranes, serve to connect different parts with each other, particularly bones and muscles; hence their division, by some anatomists, into ligaments of bones-as the ligaments of the joints; and ligaments of muscles,-as the tendons and aponeuroses.

5. Vessels are solids, having the form of canals, in which the fluids circulate. They are called-according to the fluid they convey-sanguineous (arterial and venous), chyliferous, lymphatic, &c.

6. Nerves are cords, consisting of numerous tubular fasciculi. These are connected with the brain, spinal marrow, or great sympathetic. They are the organs by which impressions are conveyed to the nervous centres, and by which each part is endowed with vitality. There are three great divisions of the nerves,—the cerebro-spinal, true spinal, and organic.

7. Ganglions are solid knots in the course of a nerve which seem to be formed of an inextricable interlacing of nervous filaments. The term is likewise applied, by many modern anatomists, to similar interlacings of the ramifications of lymphatic vessels. Ganglions may, consequently, either be nervous or vascular; and the latter, again, may be divided into chyliferous or lymphatic, according to the kind of vessel on which they appear. Chaussier, a distinguished anatomist and physiologist, has given the name glandiform ganglions to certain organs whose nature and functions are unknown, but which appear to be concerned in lymphosis, as the thymus gland, the thyroid gland, &c.

8. Follicles or crypts are secretory organs, shaped-when simple-like membranous ampullæ or vesicles, formed by an inversion of the outer membranes of the body-the skin and mucous surfaces-and secreting a fluid intended to lubricate them. They are often divided into the simple or isolated; the conglomerate; and the compound, according to their size, or the manner in which they are grouped and united together.

9. Glands are secretory organs not differing essentially from the last. Their organization is more complex; and the fluid, after secretion, is poured out by means of one or more excretory ducts.

10. Membrane.-This is one of the most extensive and important of the substances formed by the areolar tissue. It is spread out in the shape of a web; and, in man, serves to line cavities and reservoirs; and to form, support, and envelope organs.

Bichat divides membranes into two kinds, simple and compound, according as they are formed of one or more layers.

Simple membranes are of three kinds, serous, mucous, and fibrous. 1st. Serous membranes constitute all the sacs or shut cavities of the body,-those of the chest and abdomen, for example.