Bladder.—It is a hollow, membranous viscus, triangular and flattened against the pubes when empty, ovoid when distended, and in front of and upon the rectum.
Circle of Willis.—The communications established between the anterior cerebral arteries in front and the internal cavities and posterior cerebral arteries behind, by the communicating arteries, constitute the remarkable vascular communication at the base of the brain called the circle of Willis.
OF ANIMAL CHEMISTRY.
SECTION ONE.
The purpose of the present chapter, so far as our knowledge extends, is to describe the chemical history of those bodies which are characterized as being rather organized than organic; as constituting not merely a product of the vital operations of the being, but the mechanism itself by which these vital operations are carried on; as making part of the tissues essential to its proper organization and life; and as being, while in connection with the animal and participating in its life, protected from the truly chemical reactions of their proper elements, which after the death of the animal, especially when in contact with air or water, rapidly assume simpler forms of union, and breaking up the complex animal tissue into a crowd of binary compounds, under the change well known as putrefaction.
In connection with these substances which form the basis of the organs and tissues of the animal frame, will be brought under survey the processes by which, from the atmosphere or from the materials of our food, the substance of our organs is continually renewed, their growth provided for, and the conditions necessary for the continuance of life and health maintained. The following elucidation of the materials which enter into the composition of the human body is of extreme importance, as it will help to demonstrate why the chemicals employed in the former processes of embalming have been selected in preference to others.
Of Fibrine.—This substance constitutes the basis of the muscular tissue, and forms an important constituent of the blood. In the latter it exists dissolved during life, but separates after death or extraction from the body, producing, with the coloring material, the phenomenon of coagulation. In the muscles the fibrine is arranged in a truly organized and living condition, constituting the contractile fibres, in which it is so interwoven with nervous and vascular filaments as to render its isolation impossible. To obtain pure fibrine, therefore, we have recourse to blood, which, if immediately on being drawn it be briskly agitated with a little bundle of twigs, does not coagulate, but the fibrine is deposited on the twigs in soft, tenacious masses, which, being washed to remove any adhering coloring matter, and digested in alcohol and ether to remove any traces of fatty substances which may adhere to it, constitute pure fibrine; which may be dried by a gentle heat, and appears then as a yellowish, opaque mass, hard, tasteless and inodorous. If it be at all transparent, this results from traces of adhering fat. It is insoluble in water, alcohol and ether; it absorbs, however, so much water as to treble its weight, and thereby recovers the volume, softness and flexibility it possessed before being dried.
If sulphate of soda or nitrate of potash be added to newly drawn blood, its coagulation is prevented; and if fibrine be digested in a strong solution of nitre, it dissolves, forming a thick liquid, which is coagulated by heat, by alcohol, by acids, and is precipitated by the salts of mercury, lead and copper, and by yellow prussiate of potash. This property of fibrine will again come under our notice.
Of Albumen.—This substance is even more extensively distributed through the animal frame than fibrine. Like fibrine, it exists in two conditions, one soluble and one insoluble in water; but whereas the fibrine becomes insoluble almost instantly on being withdrawn from the body, albumen may retain that state for an indefinite time, and its history is therefore more complete. In its soluble form it exists in the blood, in the serous secretions, in the humours of the eye; in the soluble or coagulated form it constitutes a portion of most of the solid tissues.
Soluble Albumen.—This is obtained in the solid form by evaporating to dryness, at a temperature which does not exceed 120°, the serum of blood; the dry mass is yellow, transparent, hard, tough, and contains, besides the albumen, the salts and some other constituents of the blood in minute quantities; these are extracted by digestion in alcohol and ether, which leave the albumen pure. When thus completely dry it maybe heated beyond 212° without passing into the coagulated condition; if digested in cold water it gradually swells up and finally dissolves. This solution, when heated to a temperature between 140° and 150°, coagulates; if dilute, the solution may even be heated to 165° without coagulating, and when present in very small quantity the albumen may not separate until the water boils.