Primitive fibrils from a fibre, or primitive fasciculus; 600 times mag- by altering the focus the dark part becomes light and the light dark. Bloodvessels are exceedingly numerous in voluntary muscles, and form a fine network among the fibres. None of the branches penetrate the sarcolemma. In the illustration the arrangement is very correctly shown. Vessels of muscular tissue, from an injected preparation. Nerve fibres are said to be distributed to the elementary fibres of striated muscle. In connection with the minute nerve twigs little oval bodies are found, and are considered to be the means of communication between the nerves and fibres of the muscle. Involuntary Muscle, Striated Variety.—A portion of a heart should be boiled for a few minutes in acetic acid, and afterwards dissected and carefully teazed out in the manner directed for the preparation of voluntary fibres; the transverse striæ will readily be distinguished; even in an unprepared heart there is ordinarily no difficulty in seeing them. In the sheep's heart branching fibres may often be observed. Dr. Harley has distinguished smooth muscular fibres in the heart of the bird. The fibres of the heart in the early embryo are non-striated, being composed of elongated cells with nuclei, which are rendered very distinct by a drop of acetic acid. Non-striated Variety.-Non-voluntary muscle exists in all parts where movements occur independently of the will; in the walls of the intestinal tube; in the trachea and bronchia; in the bladder and ureters; in the uterus and corpora cavernosa; in the ciliary muscle and in the iris; in the middle coat of arteries; and in parts of the skin. The fibres of involuntary muscle are united to form fasciculi of various sizes, which cross and interlace in all directions, the fibres only running in a straight course and parallel to each other. For the purpose of examination take a piece of intestine, and macerate it for two days in a mixture of nitric acid, one part to four parts of water. This causes the tissues to swell and become yellow, while it renders the separation of the fibres more easy. A small portion of the specimen should then be cut from the edge by means of curved scissors, and teazed well out in a little water on the slide; the covering glass is to be applied in the usual way, and the object examined under a high power. Non-striated fibres are pale in colour, round or prismatic in shape, but easily flattened by pressure. In size they vary from 7000 to 3500 of an inch in diameter. They are marked at short intervals by oblong corpuscles. If the preparation has been properly made, a number of pale fibres with nuclei will appear, as in the drawing, which is taken from a preparation of the muscular coat of the human colon treated with acetic acid. Non-striated elementary fibres from the human colon. a. Treated with The substance of the fibre is translucent or finely granular, the granules being arranged in longitudinal lines. Occasionally faint striæ are seen, particularly in the fibres of the fœtal heart. Some authorities consider involuntary fibres to be constituted of elongated nucleated cells cemented together. In examining the foetal heart, the separation of fibres into elongated cells is very distinctly seen under a moderately high power. THE INTEGUMENT. THE skin consists of connective tissue, with numerous nerves and vessels, and an external covering of cells. By means of sections, which are easily made, the student may examine the constituents of the skin in their relative position, and subsequently, by scraping from the surface, and by teazing out portions of the deep-seated structures, he will be enabled to investigate the elements separately. In order to make sections, a portion of the integument of any animal must be slowly dried until sufficiently firm to bear the pressure of the razor. When properly prepared it may be cut as readily as a piece of soft horn. Thin slices should be cut with the razor, and transferred to a drop of water on the slide. In a few seconds the section will be seen to imbibe the fluid and become spread out flat upon the glass, having regained, in great part, its natural appearance. The thin covering glass must next be applied in the usual way, the specimen examined, first with a low power. and If the section has been properly prepared the several parts will be apparent, as shown in the illustration (fig. 62). 1. The epidermis, or cuticle, or scarf skin. 2. The dermis or cutis vera, or true skin. 3. Hairs, with their follicles, glands, and ducts, more or less perfect, according as the preparation is successful. The epidermis is entirely composed of epithelial scales. It is insensible and non-vascular, containing neither nerves nor vessels; the only structural objects visible in it, besides the hairs and their follicles, are the tubes of the perspiratory and sebaceous glands, and even these are seldom seen until the specimen has been specially prepared with oil of turpentine. The palms of the hand and the soles of the feet are covered with the thickest layers; sometimes in these situations it is horny as well as thick. The cells forming the cuticle are arranged in irregular rows. In the deepest layers the cells are oblong or prismatic and set vertically, the succeeding ones are round, and, like the deeper Vertical section through the skin of the ball of the thumb, transversely cells, dark in colour, containing granular matter, with wellmarked nuclei. As they approach the surface they become flattened, lighter in colour, from the removal of their granular contents, hard, dry, and insoluble in acetic acid. To render the cellular character of the epidermis more apparent, a drop of liquor potassæ should be allowed to flow under the covering glass and act slowly on the skin. In a short time the epidermis will be seen to swell, and the cells gradually separate from each other, permitting their characters to be clearly made out. Layer upon layer will be observed to cover the papillæ of the true skin, following their undulations with unvarying regularity. The pigment cells in the skin of the negro are principally found in the rete mucosum, so that when a portion of this skin is |