other more or less rapidly. It is, however, not absolutely necessary, in order to produce the contractions, that the current passing over the nerve should be closed or open, since by this means only the greatest oscillations of the current are produced; more limited variations in the intensity of the current are sufficient for physiological effects: for example, if we suddenly increase or decrease the intensity of the current, or if we suddenly conduct away by a closed circuit a portion of the current that passes over a nerve, or if we conduct, as is the case with Remak's "labile" currents, with the current generators slowly over the surface of the body; in short, if we in any way change the resistance, or if we, by chemical irritation, etc., modify the arrangement of the nerve molecules.

If a muscle be subjected to the action of an interrupted current, only that portion will contract either exclusively or at least much more energetically-that comes in direct contact with the conductors. As a consequence, in order to irritate a broad muscle by direct action completely and evenly, we must, little by little, bring the conductors into contact with all its fibres. The experiments of A. Fick' have also demonstrated that, if an irritant reaches a bundle of muscular fibres only in a limited portion of its length, it contracts only in such portion of its length-the irritated condition, consequently, does not extend over the whole length of the muscle and that in like manner, by the application of the multiplicator to a portion of the muscle not contracted, the quiescent current continues unchanged, while the contracted portion shows the negative-current oscillation.

Duchenne called the susceptibility of the muscles to contract under the direct action of the current electro-muscular contractility, in contradistinction to the indirect action, that is, the irritation of the nerve, called by Flourens motricity.

1 Ueber theilweise Reizung der Muskelfasern in Moleschott's Untersuchun gen zur Naturlehre des Menschen, vol. ii., p. 62, et seq.

The phenomena of the muscular contractions are accompanied by a peculiar sensation. Duchenne calls the power to experience this sensation, electro-muscular sensibility. It has not yet been decided whether this sensibility is due to the sensitive nerve-fibres which are found in all nerves, even the motor, or whether it is due to the sensitive nerves of the tissue surrounding the muscle, as Remak' is inclined to believe, or finally, whether the muscle-nerves themselves produce the sensation, as Eckhard' thinks possible.

The relation of the electro-muscular contractility and sensibility varies in different individuals. Every muscle, in a normal condition, possesses a certain amount of both. Sometimes, however, there is a slight difference between the same muscles of the two sides of the body. In diseased conditions, both, or each separately, may more or less completely disappear; and thus they become an important aid in diagnosis. But this we shall fully consider in Section VIII.

The gradual difference of the electro-muscular contractility and sensibility between the various muscles of the same individual is caused partly by anatomical relations— for example, in the case of the preponderance of the flexors of the hand over the extensors, we require a more powerful current to produce a contraction of the extensor digt. com. than a contraction of the flexor digt. com.-partly by the greater or less abundance of the sensitive fibres that are distributed to the motor nerves, and come in contact with the conductors; and partly by the difference of the resistance offered by the cellular tissue covering the irritated muscle; and, above all, by the thinner or thicker epidermis. Thus the muscles of the face are generally very sensitive, and above all the frontalis, because it lies immediately on the bone, and consequently, in faradizing it, the bone is also electrized, and thus a peculiar pain in the bone will be experienced together with the pain in the muscle. Then fol

1 Ueber methodische Electrisirung gelähmter Muskeln, Berlin, 1855, p. 19. Grundzüge der Physiologie des Nervensystems, Giessen, 1854, p. 113.

low the orbicularis palpebr., the levator labii sup. alæque nasi; then the sphincter oris, the levator ang. oris, the quadratus and triangularis menti; and finally, the zygomatici, the masseter, buccinator, etc. On the neck, the platysma myoides possesses an unusual degree of electro-muscular contractility and sensibility, also the sterno-cleido-mastoideus; on the other hand, the muscles of the back and abdomen are but slightly sensitive. The anterior muscles of the forearm possess far greater electro-muscular contractility and sensibility than the posterior muscles. The extensor digt. com., extensor carpi uln., etc., possess a very low grade. Finally, the tensor fascia latæ and the muscles of the inner portion of the thigh are much more susceptible than the muscles of the outer and posterior portions, partly on account of the greater supply of sensitive nerves in the skin and on account of the large quantity of sensitive fibres distributed to the part by the nervus obturatorius, partly on account of the thinner epidermis, and partly on account of the more superficial situation-while the electric current, in order to reach the muscles of the outer portion of the thigh, must pass through a thick epidermis, a thin layer, comparatively poor in sensitive nerve-fibres, and a thick layer of adipose and cellular tissue.

The contractions that arise by direct or indirect galvanic action are accompanied by a notable increase of temperature. Matteucci' found that, by the simple contractions of the muscles in the frog, after the circulation had entirely ceased, the temperature was increased 1° C.; Ziemssen, after a series of careful experiments, concludes that the muscle-contractions caused by faradic irritation of the motor nerves increase the temperature in the contracting muscles and in the skin of the part according to the grade and duration of the action. He was able, in a séance of nineteen. minutes (see Experiment IV.), during which he let the cur

1 Ueber Muskelcontraction-Referat aus: Proc. of the Royal Society, 1856. Vol. viii., No. 22, in Virchow's Archiv, 1857. Band xii., Heft I., p. 118.

rent act ten minutes, including interruptions, to cause an increase of temperature of 4.4° C. In the first minute of the muscular contraction, the mercury fell almost invariably from 0.1 to 0.5° C.; it rose, however, in the third minute, if the contraction was prolonged, and then continued unchanged. When the contractions were of moderate duration, after they had ended, the mercury rose in the first minute. most rapidly, but reached its maximum height at the first irritation always in from four to six minutes; at the later irritations, it reached its maximum height somewhat sooner. The increase in temperature was accompanied by an increase in volume, which, when the extensors were contracted in the forearm, amounted to fromto 1 cm., in the thigh to from 1 to 2 cm. Heidenhain' has lately shown that the above-mentioned sinking of the temperature at the beginning of the contractions has its cause in the imperfection of the experiments, and that the temperature immediately rises with the appearance of tetanization, at first slowly, then more rapidly. The tetanus is followed by an increase of warmth caused by oxidation which is produced by the muscular contractions, and seems to promote the circulation in so far, only, as it furnishes material for the oxidizing process.

If a motor nerve be subjected to the action of a CONSTANT CURRENT at the moment when the circuit is closed and at the moment it is opened, the muscle supplied by the nerve will contract closing contraction-opening contraction. During the time the constant battery is closed, an effect is either not at all or in a much slighter degree noticeable. Remak' arrived at the following results: 1. Tonic muscle contractions may also be produced by the constant current,

1 Mechanische Leistung, Wärmenentwicklung und Stoffumsatz bei der Muskelthätigkeit. Ein Beitrag zur Theorie der Muskelkräfte. Leipzig, 1864. 2 L. c., p. 56, et seq.

but it is necessary to conduct a powerful and painful current over the nerve (from 20 to 50 of Daniell's elements). 2. A current can cause unbearable pain, without producing a tonic contraction, while in another individual, or in the same individual at another time, the same current produces powerful contractions, and very little or no pain. 3. The production of the contractions was generally facilitated by the sudden application of the electrodes to the nerve; cases occurred, however, in which the contractions did not begin in the compass of the nerve until the conductor was slowly withdrawn from the nerve, with which it had been for about a minute in contact. The contractions continued as long as the conductor acted on the nerve by contact with the skin. 4. If the contractions did not appear at the first contact, they often did at the second, after the current had traversed the nerve for a minute or more. Remak called the contraction produced by the constant current in the manner described the galvano-tonic contraction, to distinguish it from the tetanic or clonic contraction, which is produced by frequent induction-shocks, or by the frequently-interrupted constant current. With regard to the explanation of these phenomena, according to Remak, the galvano-tonic contractions, produced in the human organism by the action of the constant current on a nerve, belong to the list of the phenomena resulting from the variations of the current intensity, to which Du Bois's law concerning the current oscillation, already given, is likewise applicable. Remak observed that the tetanus did not appear, however powerful the current, unless the electrodes were connected with the limbs by moist threads, or were in direct contact with the muscles. But if the irritability of the muscular fibres be increased, they undergo a delicate twitching, which prevents the nerve being acted upon in a similar manner. The bearing of the nerve will therefore be the same as when it is alternately brought near to and removed from the most dense current, without ever being entirely