It can be shown to exist in the blood of the hepatic vein as well as in a decoction of the liver substance, by means of either Trommer's or Fehling's tests, even when the blood of the portal vein does not contain a trace of sugar.

Origin and Destination of Glycogen. Glycogen appears to be formed de novo in the liver cells, from materials derived from the food, whether the diet be animal or vegetable, though a larger per cent. is formed when the animal is fed on starchy and saccharine, than when fed on animal food. The glucose, which is one of the products of digestion, is absorbed by the blood vessels, and carried directly into the liver; as it does not appear in the urine, as it would if injected at once into the general circulation, it is probable that it is detained in the liver, dehydrated and stored up as glycogen. The change is shown by the following formula: Water. Glycogen. C6H12O6H2O = C6H10O5.

Glucose.

:

The glycogen thus formed is stored up in the hepatic cells for the future requirements of the system. When it is carried from the liver it is again transformed into glucose by the agency of a ferment. Glycogen does not undergo oxidation in the blood; this takes place in the tissues, particularly in the muscles, where it generates heat and contributes to the development of muscular force.

Glycogen, when obtained from the liver, is an amorphous, starch-like substance, of a white color, tasteless and odorless, and soluble in water; by boiling with dilute acids, or subjected to the action of an animal ferment, it is easily converted into glucose. When an excess of sugar is generated by the liver, it can be found, not only in the blood of the hepatic vein, but also in other portions of the body; under these circumstances it is eliminated by the kidneys, appearing in the urine, constituting the condition of glycosuria.

The nervous system influences the production of the glycogenic matter; irritation of the medulla oblongata, between the auditory and pneumogastric nerves, is followed by an increase in the production of sugar, and its appearance in the urine, which, however, is only temporary.

SKIN.

The Skin, the external investment of the body, is a most complex and important structure, serving (1) as a protective covering; (2) an organ for tactile sensibility; (3) an organ for the elimination of excrementitious

matters.

The Amount of Skin investing the body of a man of average size is about twenty feet, and varies in thickness, in different situations, from the % to the of an inch.

The skin consists of two principal layers, viz., a deeper portion, the Corium, and a superficial portion, the Epidermis.

The Corium, or Cutis Vera, may be subdivided into a reticulated and a papillary layer. The former is composed of white fibrous tissue, nonstriated muscular fibres and elastic tissue, interwoven in every direction, forming an areolar network, in the meshes of which are deposited masses of fat, and a structureless amorphous matter; the latter is formed mainly of club-shaped elevations or projections of the amorphous matter, constituting the papilla; they are most abundant, and well developed, upon the palms of the hands and the soles of the feet; they average the of an inch in length, and may be simple or compound; they are well supplied with nerves, blood vessels and lymphatics.

The Epidermis or scarf skin is an extra-vascular structure, a product of the true skin, and composed of several layers of cells. It may be divided into two layers, the rete mucosum or the Malpighian layer, and the horny or corneous.

The former closely applies itself to the papillary layer of the true skin, and is composed of large, nucleated cells, the lowest layer of which, the "prickle cells," contain pigment granules, which give to the skin its varying tints in different individuals and in different races of men; the more superficial cells are large, colorless, and semi-transparent. The latter, the corneous layer, is composed of flattened cells, which, from their exposure to the atmosphere, are hard and horny in texture; it varies in thickness from % of an inch on the palms of the hands and feet, to the o of an inch in the external auditory canal.

APPENDAGES OF THE SKIN.

Hairs are found in almost all portions of the body, and can be divided into (1) long, soft hairs, on the head; (2) short, stiff hairs, along the edges of the eyelids and nostrils; (3) soft, downy hairs, on the general cutaneous surface. They consist of a root and a shaft, which is oval in shape, and about the of an inch in diameter; it consists of fibrous tissue, covered externally by a layer of imbricated cells, and internally by cells containing granular and pigment material.

The Root of the hair is embedded in the hair follicle, formed by a tubular depression of the skin, extending nearly through to the subcutaneous tissue;

its walls are formed by the layers of the corium, covered by epidermic cells. At the bottom of the follicle is a papillary projection of amorphous matter, corresponding to a papilla of the true skin, containing blood vessels and nerves, upon which the hair root rests. The investments of the hair roots are formed of epithelial cells, constituting the internal and external root sheaths.

The hair protects the head from the heat of the sun and cold, retains the heat of the body, prevents the entrance of foreign matter into the lungs, nose, ears, etc. The color is due to the pigment matter, which, in old age, becomes more or less whitened.

The Sebaceous Glands, imbedded in the true skin, are simple and compound racemose glands, opening, by a common excretory duct, upon the surface of the epidermis or into the hair follicle. They are found in all portions of the body, most abundantly in the face, and are formed by a delicate, structureless membrane, lined by flattened polyhedral cells. The sebaceous glands secrete a peculiar oily matter, the sebum, by which the skin is lubricated and the hairs softened; it is quite abundant in the region of the nose and forehead, which often present a greasy, glistening appearit consists of water, mineral salts, fatty globules, and epithelial cells. The Vernix caseosa which frequently covers the surface of the foetus at birth consists of the residue of the sebaceous matters, containing epithelial cells and fatty matters; it seems to keep the skin soft and supple, and guards it from the effects of the long continued action of water.

ance;

The Sudoriparous Glands excrete the sweat; they consist of a mass or coil of a tubular gland duct, situated in the derma and in the subcutaneous tissue; average the of an inch in diameter, and are surrounded by a rich plexus of capillary blood vessels. From this coil the duct passes in a straight direction up through the skin to the epidermis, where it makes a few spiral turns and opens obliquely upon the surface. The sweat glands consist of a delicate homogeneous membrane lined by epithelial cells, whose function is to extract from the blood the elements existing in the perspiration.

The glands are very abundant all over the cutaneous surface, as many as 3528 to the square inch, according to Erasmus Wilson.

The Perspiration is an excrementitious fluid, clear, colorless, almost odorless, slightly acid in reaction, with a specific gravity of 1.003 or 1.004.

The total quantity of perspiration excreted daily has been estimated at about two pounds, though the amount varies with the nature of the food and drink, exercise, external temperature, season, etc.

The elimination of the sweat is not intermittent, but continuous; but it takes place so gradually that as fast as it is formed it passes off by evaporation as insensible perspiration. Under exposure to great heat and exercise the evaporation is not sufficiently rapid, and it appears as sensible perspiration.

Carbonic acid is also exhaled from the skin, the amount being about zoo of that from the lungs.

Perspiration regulates the temperature, and removes waste matters from the blood; it is so important, that if elimination be prevented death occurs in a short time.

The Nervous System influences the secretion of watery vapor by causing a dilatation of the capillary blood vessels around the tubular coil. It is increased by mental emotions; section of the sympathetic fibres in the neck is followed by a copious perspiration; stimulation of the nerves, producing contraction of the vessels, is followed by an arrestation of the elimination of the sweat.

NERVOUS SYSTEM.

The Nervous System co-ordinates all the various organs and tissues of the body, and brings the individual into conscious relationship with external nature by means of sensation, motion, language, mental and moral manifestations.

The Nervous Tissue may be divided into two systems, viz: the Cerebro-spinal and the Sympathetic.

(1) The Cerebro-spinal System occupies the cavities of the cranium and spinal canal, and consists of the brain, the spinal cord, the cranial and spinal nerves. It is the system of animal life, and presides over the functions of sensation, motion, etc.

(2) The Sympathetic System, situated along each side of the spinal column, consists (1) of a double chain of ganglia, united together by nerve cords, which extends from the base of the cranium to the coccyx; (2) of various ganglia, situated in the head and face, thorax, abdomen, pelvis, etc. All the ganglia are united together by numerous communicating fibres, many of which anastomose with the fibres of the cerebro-spinal system. It is the nervous system of organic life, and governs the functions of nutrition, growth, etc.

Nervous Tissue is composed of two kinds of matter, the gray and white, which differ in their color, structure and physiological endowments; the former consists of vesicles or cells which receive and generate nerve force; the latter consists of fibres which simply conduct it, either from the periphery to the centre or the reverse.

Structure of Gray Matter. The gray matter, found on the surface of the brain in the convolutions, in the interior of the spinal cord, and in the various ganglia of the cerebro-spinal and sympathetic nervous systems, consists of a fine connective-tissue stroma, the neuroglia, in the meshes of which are embedded the gray cells or vesicles.

The cells are grayish in color, and consist of a delicate investing capsule containing a soft, granular, albuminous matter, a nucleus, and sometimes a nucleolus. Some of the cells are spherical or oval ́in shape, while others have an interrupted outline, on account of having one, two, or more processes issuing from them, constituting the uni-polar, bi-polar or multipolar nerve cells. Cells vary in size; the smallest being found in the brain, the largest in the anterior horns of gray matter of the spinal cord. Some of