Page:The American Cyclopædia (1879) Volume I.djvu/553

ANIMAL ELECTRICITY 521 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, indi- cating the passage of a galvanic current. Ac- cording to the discoverer of this important fact, at the time of the contraction of the mus- cles of one arm, the current which existed there, and which was neutralized by a cur- rent of equal strength in the other arm, be- comes 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 electro- motive 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 transverse 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 sec- tions, may show their electro-motive power without being divided. However, the electro- motive power of the undissected muscles is often more or less concealed by the contrary action of a layer situated on the natural trans- verse section, which Du Bois-Reymond calls the parelectronomic layer. The contrary elec- tro-motive power of this layer may be increased by cooling the animal. 5. Every minute parti- cle 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, &c. 8. We may add that, according to Brown-Sequard, the electro-mo- tive power, at least in muscles, after it has disappeared naturally after death, may be re- produced with the other vital properties by the influence of injections of oxygenated blood. 9. In the different contractile tissues the elec- tro-motive power is always proportioned to the mechanical power of the tissue. 10. Other animal tissues may produce electro-motive ac- tion ; 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 sud- den variations of intensity and direction, which may be thus briefly stated : 11. The galvanic current in muscles when in the act of contrac- tion, and in nerves when conveying motion or sensation, undergoes a sudden and great dimi- nution 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 par- electronomic layer, when contracting, become active in the opposite direction to that which muscles in a state of rest exhibit. Hence it must be concluded that the electro-motive force of the parelectronomic layer remains con- stant in the act of contraction. 13. If any part of a nerve is submitted to the action of a per- manent current, the nerve in its whole extent suddenly undergoes a material change in its internal constitution, which disappears on breaking the circuit as suddenly as it came on. 14. The electrical phenomena of motor and sensitive nerves are identical. Both classes of nerves transmit irritation in both directions. We will merely say in addition to these laws, that, in examining who was right between Galvani and Volta, we find that they were both in some points right, and in some others wrong. Galvani was right in saying that there is an animal electricity, and Volta was right in looking at the heterogeneity of metals as a source of electricity ; and had he extended his views to the living tissues, he would have found that there also, as in metals, where there are two heterogenic particles in contact one with the other, a galvanic current is generated. II. The production of static electricity in animals. A constant production of this kind of electri- city cannot be doubted ; but animals and men j being in free communication with the earth, | it is rarely possible to ascertain the presence of this electricity. But when the body of a man is insulated he may affect the electrome- ter. If two men are insulated, as it often oc : curs that they are charged with different elec- tricities, there is when they touch each other a peculiar crackling, and sometimes a spark, announcing the combination of the vitreous and the resinous electricity. In dry weather many persons may hear the sound and see the light resulting from a combination, when they suddenly pull off the articles of dress in contact with their skin. Dr. Schneider men- tions a Capuchin friar who, on removing his cowl, used to perceive a number of shining,