whether this is due to fibres of this system passing up through the cord, or to the action of that nervous centre itself. If one-half of the cord be divided, the limb on the same side has its vessels soon dilated, its sensibility augmented, and its temperature increased, so that the vaso-motor fibres do not decussate till the pyramids, where the ordinary motors also cross. Again, Lister has shown that irritation of the cord in the frog will produce contractions of the vessels of the web, and the same effect may be produced by galvanising the anterior roots of the sciatic nerve within the canal of the large edible frog. Division of the roots produces dilatation of the vessels, increased circulation, and more rapid absorption of poisons. Some recent experiments show, that section of the cerebro-spinal nerves which join the sympathetic produces the effects upon the eye usually assigned to section of the sympathetic; and if the latter nerve be divided between ganglia, no effect on the eye follows. Brown-Séquard believes that irritation of a centripetal nerve may produce either constriction or enlargement of remote vessels; and I quote from him the following passage, as showing the great pathological interest of these inquiries: "Suppose a worm in the bowels irritating their centripetal nerve fibres, the irritation is propagated to the spinal cord, which reflects it upon the roots of the cervical sympathetic nerve, by which it reaches the bloodvessels of the retina, produces their contraction, and, as a consequence of this cause of diminution in the amount of blood, an amaurosis. If, instead of the reflex action on the blood-vessels there is an action on the tissues, as in the case of the experiments of Bernard, the bloodvessels dilate and more blood passes through them. The cornea, for instance, is irritated; its centripetal nerve fibres transmit the irritation to the pons varolii, which reflects it upon the retina, the lacrymal gland, the conjunctive, &c.; more blood is attracted by all these parts, their blood-vessels dilate, and the consequences of a greater amount of blood becomes manifest-increase of tears, photophobia, &c." Du Bois Reymond assigns as the cause of hemicrania, from which he suffers intensely, tetanic contraction of the arteries of the affected side produced by the sympathetic. We shall return to this subject when reviewing the pathology of innervation. QUESTIONS FOR EXAMINATION. JUNIOR. 1. What is the composition of brain matter, and does it vary with the superiority of its function? 2. Describe the structure of a nerve-tube. 3. Do nerves anastomose, and in what way do they terminate? 4. What proofs can you offer that divided nerves re-unite? 5. Enumerate the electric fishes, and show that the agent they emit is identical with electricity set free by ordinary means. 6. State the uses of the membranes of the cerebro-spinal axis, noting any differences which occur in different parts of it. 7. Describe the external form of the cord. 8. Mention any experiments which show the functions of the cord. 9. What are the functions of the roots of the spinal cord, and how can they be shown? 10. What functions have been assigned to the cerebellum ? 11. Enumerate the cranial ganglia and the commissures between them. 12. What functions have been assigned to the sympathetic system? SENIOR. 1. Sketch the histology of dynamic neurine. 2. Contrast the position and structure of gelatinous and cylindrical nerve-tubes. 3. Explain the structure and uses of a ganglion and a plexus. 4. What theories of nervous force have been started, and in what particulars do it and electricity seem to differ and to agree? 5. Say what you know of the luminosity of animal bodies. 6. Are the quantity of blood and superincumbent pressure of the brain the same at all times? Give any facts and arguments which bear on the questions. 7. Sketch fully the appearances seen upon a transverse section of the cord visibly and microscopically. 8. Explain and illustrate reflex nervous phenomena in health and disease. 9. What are the effects of section of one half of the spinal cord ? 10. Describe the structure and functions of the medulla oblon gata. 11. Adduce as many arguments as you can for and against phrenology. 12. Enumerate and explain the effects which follow section of the cervical portion of the sympathetic system? What other section is said to produce similar effects on the eye? MOTION Is exhibited in animal bodies, usually in three waysmolecular, ciliary, and muscular; the first of which is common to the vegetable and inorganic kingdoms, and was discovered by Robert Brown, after whom it is often named. It is easily seen when fine particles are suspended in a fluid; gamboge when rubbed up in water shows it readily. The movements called cyclosis in the characea-which are, however, very regular and not influenced by evaporation-and that of the pollen of plants, may be of this nature. It has been said to be due to currents produced by evaporation (it will sometimes, however, go on in vessels hermetically sealed, or in oil which is not volatile), by the light heating the surface of the fluid, by vibrations produced in the room where the vessels lie, or by gravitation. The movements of the bloodcells, and of the fibres of Jacob's membrane, are sometimes regarded as molecular. Ciliary Motion may be seen on the lachrymal, nasal, and bronchial surfaces, on that of the Fallopian tubes, and for a few lines on the peritoneum where they end in the fimbriæ, and on the minute seminiferous and uriniferous passages. Cilia are much more abundant in the lower forms of animal life, serving for the introduction of nutritive matter and the removal of that which is effete. The only serous membrane which is ciliated in man is the arachnoid in the ventricles; but the pericardium, peritoneum, &c., are ciliated in reptiles. Cilia are about 1000 in length, are thickly set in rows on columnar epithelium. Those of the tracheal cells are shown upon p. 152. Their motion is very remarkable when watched by the microscope; they wave usually towards orifices, and all bend at once, like corn when affected by the wind, sometimes they sweep round, like the feathering of an oar. A little powdered charcoal makes their movements more apparent. They move long after muscular motion has ceased; thus, the tracheal cilia of man have been seen to wave 7 days after death, and those of the œsophagus of the turtle 19 days, when the body was becoming putrid. Ciliary motion is best preserved by a uniform degree of moisture and temperature, and continues longest in blood-whereas bile checks it at once. appears to be independent of muscular or nervous force, as it remains so long after their departure, and even upon one separated epithelial cell; and electricity, prussic acid, or opium, do not affect it. Spermatozoa are regarded by some as cells with single cilia. The enlargement and contraction of the cell by osmose is probably the cause of the motion of the cilia; and such motions in plants as the folding of the leaves of the sensitive plant, the bending of the stamens of the barberry, and the closing of the venus's fly-trap, are believed to be analogous. It Locomotion is a faculty possessed by nearly all animals, and there is nothing analogous among plants. In man, the organs concerned in this function are either active-as the muscles, under the command of the cerebro-spinal system-or passive, including the bones, with the ligaments which bind them together; the cartilages, which render their ends smooth and elastic; the syno vial membranes, which obviate friction; and the areolar and adipose tissues, which connect, yet separate and pack all the apparatus of motion. Fibrous Tissue, which composes all ligaments, tendons, fasciæ, and areolar matter, is of two kinds—1. White, inelastic threads placed parallel to each other, like a skein of silk, and loosely connected by areolar tissue. Acetic acid swells and softens the fibres, and, by bringing nuclei into view, shows that it was developed in cells arranged lineally. Gelatin is produced by boiling. Its physical properties are, a glistening silvery whiteness, flexibility, and such tenacity that 1,000 lb force is required to rupture the tendo achillis. The strength of muscle is, however, greater during life. This tissue is but slightly vascular and sensitive during health, but its unyielding nature gives rise to great pain under inflammation. It is used in the construction of funicular, fascicular, or capsular ligaments, to bind bones together; in tendons, through which muscles act with greater efficacy, while bulk is reduced; in aponeuroses, which confine muscles; in the coating of bone and fibro-cartilage; and in protecting the brain (dura mater), brous Tissue. eye (sclerotic), testis (tunica albuginea), &c. Its reparation is accomplished by a soft blastema, which gradually assumes the fibrous character. White Fi 2. Yellow elastic tissue is made up of finer fibres, ranging from 10000 to 300, with sharp, distinct margins, and having a tendency to divide transversely, as if made up of cells. These more readily split up into 2 or 3 smaller threads which, however, exceed the diameter of the primary fibre, and which curl back on themselves, like celery dressed for table. Prolonged boiling, acids, or the digestive or putrefactive processes, but slightly affect this tissue. From being stained yellow by nitric |