rential floods induced the French Government, a few years ago, to take steps to reclothe the mountains with trees and vegetation. It is estimated that it will take one hundred and fifty years before the work contemplated is fully accomplished; but encouraging results have already followed the little that has been done.

J. Croumbie Brown states that like damage, only in less degree, is done by the mountain torrents of South Africa. One which occurred in 1868 damaged public property alone to the amount of $250,000, and private property about half a million dollars. By the floods of 1874 damage was done to the public works alone amounting to about a million and a half of dollars.

Illustrations showing the great loss of both life and property occasioned by torrential floods could be multiplied indefinitely, but the few cited ought to be sufficient to show that they are a calamity which great pains should be taken to prevent. That they are possible in the mountain regions of the United States was shown by the recent disastrous flood in Pennsylvania, when streams rose so rapidly that people were glad to escape with their lives, and lost property valued at several million dollars. While it is not to be supposed that torrents can be wholly prevented by mountain forests, it is certain that they can be modified to such an extent as to prevent their doing such serious damage.

But there are possible results following the drying up of the streams through the unlimited destruction of forests that should alarm the American people, and cause them to make greater effort to preserve the forests in localities where they now exist and their cultivation where they do not. How terrible these results may be is seen in the desolation wrought upon Babylon, Nineveh, Thebes, Memphis, and especially upon the people of the Chinese province of Shan-Li only three years ago, by the loss of their forests. History shows that not a few nations have declined with the disappearance of their forests; and upon the preservation of our watercourses may depend our existence as a nation. While the government ought to protect its own forests and especially its own mountain forests, it is the farmers and other small land-owners who can effect the most good; and every influence possible should be exerted to induce them to reclothe a portion of their denuded lands. In this work the most effective agency would be the press, particu larly the agricultural press; and it is to be hoped that it will agitate the subject until the desired result be brought about.

ON THE INFLUENCE OF THE STRUCTURE OF THE NERVE-FIBRES UPON THE PRODUCTION AND CONDUCTION OF NERVE-force. By H. D. SCHMIDT, of New Orleans, La.

IN studying the various physiological phenomena, which manifest themselves through the medium of the nervous system, the question as to the mysterious agency, causing these manifestations, as well as to the particular mode in which it operates, naturally presents itself to our mind. The older theories of the nature and propagation of nerve-force, based upon vague speculations, represented the nervous phenomena as caused by some physical agency, or principle, such as a nervous fluid or gases, running through the nerves; and it was not until the discovery of electricity that nervous force commenced to be regarded as identical with this agent, a view, which was finally corroborated by the discoveries of Galvani, and his contemporary investigators, of the electrical phenomena of animals. For Du Bois Raymond, however, it was left to show, as late as 1843, that in every portion of nerve, in a living excitable condition, an electric current, originating in the nervous substance itself, passed from its surface, or longitudinal section to the transverse, from which it returned through the nerve to complete the circuit. Nearly at the same time, this physiologist also discovered the so-called electrotonic condition, or "electrotonus" of the nerves, a discovery which greatly advanced our knowledge of the inherent properties of these nervous organs, and facilitated the investigations relating to the true nature of nerve force.

The observed fact that from the molecules of every part of the longitudinal section, or surface, of the nerve, an electric current passes to the nearest transverse section, thence back to the former, forming a circuit through the nerve, gave rise to the idea that each nerve, or, better said, nerve-fibre, consisted of innumerable electro-motor elements, each of which possessed a positive equatorial, and two negative polar zones; and that these elements, surrounded by an indifferently conducting liquid, were arranged in such a manner, as to present their positive equatorial zone to the longitudinal section, or surface, while their negative polar zones were directed toward the transverse sections. But, in order to explain the different phenomena presented by the nerve when in the electrotonic condition, this peripolar theory was modified so far as to make each of the peripolar elements consist of two di

polar molecules, the positive poles of which were to point toward each other. And, in accordance with this supposition, the increase of strength in the natural electric current of the nerve at rest was explained in presuming that the polarizing current, while passing through the nerve, caused the electrical unlike particles of the latter to arrange themselves in an order, similar to the elements of a Voltaic pile; in other words, that the positive poles turned toward the side to which this current is directed, the negative toward the side from which it comes. The polarization of the nervous molecules, therefore, was to be regarded as an electrolytic process, causing the negative poles to turn toward the positive, and the positive poles toward the negative electrode.

At the time when the above theory was established, the preexistence of the axis-cylinder of the nerve fibre was still a disputed point; and, accordingly, the theory was based upon the supposition that the entire double-bordered nerve-fibre consisted only of a basement-membrane tube, the so-called membrane of Schwann, filled with a homogeneous nervous substance, or matter. The sympathetic nerve-fibres, representing naked axis-cylinders, were hardly known as such, but were generally looked upon as a kind of connective tissue. Aside from the objections, however, which, at present might be raised against the above theory, it was insufficient to explain some of the phenomena pertaining to the electric condition of the nerve, and, for this reason, it lost its popularity and was finally displaced by more recent theories, the most prominent of which was the so-called theory of "liberation," or "discharge," of Phlueger.

This is based upon the supposition that in the molecules of a nerve a certain amount of potential energy is always present to be converted into kinetic energy; and, furthermore, that there are two antagonistic forces exerting their influence upon these molecules which are constantly inclined to motion. One of these forces is supposed to cause the motion of the molecules, while the other is believed to inhibit it. In the nerve at rest, the forces balance each other, while in the state of activity, the inhibitory force diminishes, and thus determines the degree of force liberated by a given stimulus. Accordingly, in the anelectrotonic condition of the nerve, the force inhibiting the movements of the molecules increases, while in the cathelectrotonus it diminishes. The propagation of the nerve-force, finally, is explained by each nervous element

liberating from its neighbor a certain amount of force, which increases with the continuation of the process.

Though a number of other theories regarding the mode of production and propagation of nerve-force have subsequently been advanced from time to time, that part of Phlueger's theory, which explains the production and conduction of the force in question as being effected by each nervous element liberating a certain amount of potential energy from its neighbor, the whole representing a chain of liberating processes, was generally accepted.

Hermann, who regards the liberated forces as chemical in their nature, sums up the more recent theories on the subject as follows: in every nervous particle, he says, a certain substance, containing potential force and being inclined to part with the energy it contains, splits during its state of activity; and, in consequence of this splitting, the same takes place in the neighboring element. The process of conduction in the nerve, therefore, is comparable to that going on in a train of gunpowder fired at one end; though, in order to understand why the whole store of potential force present is not consumed at once, as in the case of the powder, the presence of some inhibitory force, in some form or other, must be presumed.

It is a notable fact that in all the theories on the nature of nerve-force, be it the liberating or the preceding dipolar, the anatomical structure of the nerve-fibre, such as it has been revealed by modern histological researches, has never been taken into account; on the contrary, the explanations given by the physiologist on the subject were mostly based upon principles purely physical or chemical in their nature, making the nerve-fibre play the part of a simple, homogeneous organic wire without structure. The question, therefore, whether the medullary sheath, with its cylindro-conical segments, the annular constrictions of Ranvier in the external sheath, or the granular fibrillæ of the axiscylinder, were but the products of a fanciful freak of nature, may justly be raised. Or, could it be that the compound anatomical structure of the axis-cylinder conducted nerve-force in the same manner as a homogeneous copper-wire conducts electricity? These questions must be answered, before a satisfactory theory on the production and conduction of nerve-force can ever be established. For my part, I have always held the view that a difference of structure necessarily causes a difference of function: for, if it

were otherwise, differentiation of structure in organized beings. would hardly take place. Therefore, it may be safely presumed that the structure of a tissue is always determined by adapting itself to the function of the organ of which it forms a part. For this reason, I shall endeavor in the following pages to direct the attention to those anatomical facts, which, as yet, have not been brought into harmony with the theories existing on the mode of production and conduction of nerve-force. But, as my time does not allow me to treat the subject to its full extent, I shall for the present confine my remarks and demonstrations to the so-called double-contoured nerve-fibres, of which the peripheral nerves are chiefly composed.

A double bordered nerve-fibre consists of three principal elements, viz. the axis cylinder; the nerve-medulla, or medullary sheath; and the external sheath, or tubular membrane, also known as the sheath of Schwann. The relative position of these elements is such, that the axis-cylinder, which forms the axis of the fibre, is surrounded by the nerve-medulla, and this, again, by the external sheath. When microscopically examined in serum, -while still in connection with the living animal, or, when removed from one freshly killed,-the double-bordered nerve-fibre is distinguished, as its name indicates, by well defined doubleborders, while the part between the inner of these borders, forming the greater portion of the nerve-fibre, appears somewhat opaque, and exhibits a peculiar fatty lustre, which is owing to the refractive properties of the nerve-medulla.

In tracing one of these nerve-fibres throughout its length, it will be found that it is apparently divided into separate segments by a number of deep constrictions, the normality and true nature of which were first recognized by Ranvier a distinguished French histologist. This appearance of segmentation is due to the interruptions in the nerve-medulla, leaving the axis-cylinder, at the points of interruption, only covered by the external sheath, which, in order to reach the latter, becomes constricted at these points. The constrictions thus formed by this sheath are known as the "annular constrictions" (étranglements annulaires) of Ranvier (fig. 1, d). But, in examining a little more closely the individual segments formed by this singular interruption of the nerve medulla, it will be found that they themselves are subdivided by a number of deep incisures, observed in the medul