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 of that from the lungs.

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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.

Influence of the Nervous System.-The secretion of sweat is regulated by the nervous system. Here, as in the secreting glands, the fluid is formed from material in the lymph spaces surrounding the gland. Two sets of nerves are concerned, viz.: vasomotor, regulating the blood supply; and secretory, stimulating the activities of the gland cells. Generally the two conditions, increased blood flow and increased glandular action, coexist. At times profuse clammy perspiration occurs, with diminished blood flow.

The dominating sweat center is located in the medulla, though subordinate centers are present in the cord. The secretory fibers reach the perspiratory glands of the head and face through the cervical sympathetic; of the arms, through the thoracic sympathetic, ulnar, and radial nerves; of the leg, through the abdominal sympathetic and sciatic nerves.

The sweat center is excited to action by mental emotions, increased temperature of blood circulating in the medulla and cord, increased venosity of blood, and many drugs, rise of external temperature, exercise, etc.

NERVOUS SYSTEM.

The Nervous System coördinates 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, the Cerebrospinal 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, and 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 fibers, many of which anastomose with the fibers 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 fibers which simply conduct it, either from the periphery to the center 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 multi-polar nerve cells. Cells vary in size; the smallest being found in the brain, the