It is known that when a continuous current passes through a nerve there is a contraction in the muscle which it enters in the beginning of the passage and on its cessation, and also when there is any change in its strength. ■ It is to this last condition that the induced contraction is attributed by Du Bois-Reymond, but, if he were right, there should be a contraction in the induced muscle at the time we put its nerve on the inducing one, and also at the time we take it away; but unfortunately for the theory, there is no contraction in these cases, except in peculiar circumstances. We must therefore consider the theory of the distinguished German physiologist as not sufficiently grounded. - Whatever may be the cause of the irritation of the nerve of the induced muscle, it is certain that when the inducing one contracts this motor nerve is irritated; the same thing takes place, as Matteucci and Brown-Se-quard observe, when an excitor or a sensitive nerve instead of a motor is placed upon the inducing muscle; the irritation then causes either a reflex movement or a pain. Brown-Sequard has been led by many experiments to conclude that the irritation of sensitive nerves by the contraction of inducing muscles has a great share in many important physiological and pathological phenomena.

Every one knows that, except when we look at the parts of our body which we move voluntarily, we direct our movements almost entirely according to the sensations that we receive from our contracting muscles. These sensations have been shown by this physiologist to be chiefly due to the induced irrritation of the sensitive nerves at the time the muscles contract. The muscular sense of Sir Charles Bell, or the guiding sensations of Prof. Carpenter, are thus obtained, and so it is with the measure of the distance of objects when looked at with both eyes; the state of our ocular muscles teaches us the distance, and they do it by the irritation they induce in nerves while contracting. According to Brown-Sequard, the pain of cramps, that of the contractions of the uterus in parturition, that of the spasm of the sphincters, etc, depends upon an excessive induced irritation of the sensitive nerves in consequence of muscular contractions. Among the other proofs adduced by him in support of his view that muscular contractions, normal or pathological, induce irritations in their sensitive nerve fibres, probably by a galvanic discharge, and exactly as an inducing muscle irritates a motor nerve placed upon it, the following are the most important: He has found that it is electrically just the same thing for the intensity of the irritation of the motor nerve lying upon an inducing muscle, and for the intensity of pain in a case of spasm of the sphincter of the anus, and in a case of contraction of the anterior muscles of the thigh.

In these three circumstances, viz., the experiment with the motor nerve, and the two pathological cases in man, we observe: 1, that there is no irritation or no pain if the inducing muscle has no resistance to overcome when it contracts (it is so after the section of the muscle or of its tendon); 2, that the irritation or the pain increases when the inducing muscle is extended. The known facts that the pain due to the spasm of the sphincter of the anus disappears when it is divided, and that the section of a tendon of a contracted muscle causes the cessation of pain, had not hitherto received any explanation. The researches of Brown-Sequard render now very easy the understanding of the mode in which these facts are produced. - With the help of his very sensitive galvanometer, Du Bois-Reymond has been able to prove that the galvanic currents of muscles in man may be rendered evident during a voluntary movement. If the two electrodes of the galvanometer are in communication, one with one hand and the other with the other hand of a man, and if a voluntary movement is made by one of the arms, there is at once a deviation of the needle of the instrument, indicating the passage of a galvanic current.

According to the discoverer of this important fact, at the time of the contraction of the muscles of one arm, the current which existed there, and which was neutralized by a current of equal strength in the other arm, becomes diminished, and therefore the surplus of the other passes out and deflects the needle of the instrument. - Du Bois-Reymond has discovered that nerves are, like muscles, able to afford galvanic currents. The principal law concerning these currents is the same as that of the muscular currents. The direction of the galvanic current of the nerves is from their interior to their exterior, just as it is with the muscles. From all his experiments on the electro-motive power of muscles and nerves, the following conclusions may be drawn: 1. The muscles and nerves, including the brain and the spinal cord, are endowed during life with an electro-motive power. 2. This electromotive power acts according to a definite law, which is the same in the nerves and muscles, and may be briefly stated as the law of the antagonism of the longitudinal and transverse section; the longitudinal surface being positive, and the transversa section negative. 3. As the nerves have no natural transverse section, their electro-motive power when they are in a state of rest cannot be made apparent unless they have previously been divided. 4. The muscles, having two natural transverse sections, may show their electro-motive power without being divided.

However, the electromotive power of the undissected muscles is often more or less concealed by the contrary action of a layer situated on the natural transverse section, which Du Bois-Reymond calls the parelectronomic layer. The contrarv elec-tro-motive power of tins layer may be increased by cooling the animal. 5. Every minute particle of the nerves and muscles acts according to the same law as the whole nerve or muscle. 6. The currents which the nerves and muscles produce in circuits of which they form a part, must be considered only as derived portions of incomparably more intense currents circulating in the interior of the nerves and muscles around their ultimate particles. 7. The electro-motive power lasts after death, or, in dissected nerves and muscles, after separation from the body of the animal, as long as the excitability of the nervous and muscular fibres; whether these fibres are permitted to die gradually from the cessation of the conditions necessary to the support of life, or whether they are suddenly deprived of their vital properties, by heat, chemical means, etc. 8. We may add that, according to Brown-Sequard, the electro-mowae power, at least in muscles, after it has disappeared naturally after death, may be reproduced with the other vital properties by the influence of injections of oxygenated blood. !). In the different contractile tissues the electro-motive power is always proportioned to the mechanical power of the tissue. 10. Other animal tissues may produce electro-motive action; but it is neither so strong as the action of the nerves and muscles, nor so regular; nor does it vanish with the vital properties of the tissues; nor does it, lastly, undergo those sudden variations of intensity and direction, which maybe thus briefly stated: 11. The galvanic current in muscles when in the act of contraction, and in nerves when conveying motion or sensation, undergoes a sudden and great diminution of its intensity. (We have said above that there is some reason to doubt the accuracy of this law as regards muscles.) 12. Muscles inactive from the contrary action of the parelectronomic layer, when contracting, become active in the opposite direction to that which muscles in a state of rest exhibit.