lemma), forming a tube, through the centre of which runs the axis cylinder, which is probably_composed of an aggregation of very fine filaments. Between the axis cylinder and the tube is a fluid, rich in fatty matters, from which a solid strongly refracting substance has been thrown down and lines the tube.

FIG. 101. Smooth or non-stri.

ated muscular fibres of a small artery; the middle one having been treated with more distinctly the nucleus a. (Magnified about 350 diameters.)

from the middle coat

Such is the structure of all the larger nerve fibres, which lie, side by side, in the trunks of the nerves, bound together by delicate connective tissue, and enclosed in a sheath of the same substance, called the neurilemma. In the trunks of the nerves, the fibres remain perfectly distinct from one another, and rarely, if ever, divide. But when the nerves

enter the central organs, and when they approach their peripheral terminations, the nerve-fibres frequently divide into branches. In any case they become gradually finer and finer; until at length, axis-cylinder, sheath, and contents are no longer separable, and the nerve fibre is reduced to a delicate filament, the ultimate termination of which, in the sensory organs and in the muscles, is not yet thoroughly made out.

17. In Lesson VIII. mention is made of peculiar bodies called tactile corpuscles, which are oval masses of specially modified connective tissue in relation with the ends of the nerves in the papillæ of the skin. In Fig. 103 four such papillæ, which have been rendered transparent and stripped of their epidermis, are seen, and the largest contains a tactile corpuscle (e). mode, in which nerves not connected with tactile corpuscles end in the skin, is not definitely known.

acetic acid, shows

This

In muscles, the nerve-fibre seems to pierce the sarcolemma and to end inside the ultimate muscular fibre in a peculiar knob or plate.

In the brain and spinal cord, on the other hand, it is

certain that, in many cases, the ends of the nerve-fibres are continued into the processes of the ganglionic corpuscles. 18. The olfactory nerves are composed of pale, flat fibres

A, a nerve-fibre in its fresh and unaltered condition; B, a nerve-fibre in which the greater part of the sheath and coagulated contents (a b) have been stripped off from the axis cylinder (cc); C, a nerve-fibre, the upper part of which retains its sheath and coagulated contents, while the axis cylinder (a a) projects; D, a ganglionic corpuscle-a, its nucleus and nucleolus. (Magnified about 350 diameters.)

without any distinction into axis-cylinder and contents, but with nuclei set at intervals along their length.

Similar fibres are found in the sympathetic nerves, mingled with fibres of the same structure as those of the spinal nerves.

19. Ganglionic corpuscles are chiefly found in the cerebro-spinal axis; in the ganglia of the posterior nerve roots, and in those of the sympathetic; but they occur also elsewhere, notably in some of the sensory organs (see Lesson IX.).

They are spheroidal bodies, consisting of a soft semisolid cell substance in the midst of which is a large

FIG. 103-PAPILLE OF THE SKIN OF THE FINGER.

a, a large papilla containing a tactile corpuscle (e) with its nerve (d): , other papillæ, without corpuscles, but containing loops of vessels, c. (Magnified about 300 diameters.)

clear and transparent area usually termed the nucleus. Within the nucleus again is generally a smaller body commonly termed the nucleolus (Fig. 102, D, a). Each ganglionic corpuscle sends off one, two, or more prolongations, which may divide and subdivide; and which, in some cases, unite with the prolongations of other ganglionic corpuscles, while, in others, they are continued into nerve-fibres.

APPENDIX A.

A TABLE OF ANATOMICAL AND PHYSIOLOGICAL

CONSTANTS.

THE weight of the body of a full-grown man may be taken at 154 lbs.

The addition of 7 lbs. of blood, the quantity which will readily drain away from the body, will bring the total to 154 lbs. A considerable quantity of blood will, however, always remain in the capillaries and small bloodvessels, and must be reckoned with the various tissues. The total quantity of blood in the body is now calculated at about 1-13th of the body weight, i.e. about 12 lbs.

The solids would consist of the elements oxygen, hydrogen, carbon, nitrogen, phosphorus, sulphur, silicon, chlorine, fluorine, potassium, sodium, calcium (lithium), magnesium, iron (manganese copper, lead), and may be arranged under the heads of—

Proteids.

Amyloids.

Fats. Minerals.

Such a body would lose in 24 hours-of water, about 40,000 grains, or 6 lbs.; of other matters about 14,500 grains, or over 2 lbs. ; among which of carbon 4,000 grains; of nitrogen 300 grains; of mineral matters 400 grains; and would part, per diem, with as much heat as would raise 8,700 lbs. of water o° to 1° Fahr., which is equivalent to 3,000 foot-tons.1 Such a body ought to do as much work as is equal to 450 foot-tons.

The losses would occur through various organs, thus-by

The gains and losses of the body would be as follows :-

Creditor--Solid dry food

grs.

8,000

high.

A foot-ton is the equivalent of the work required to lift one ton one foot