CURRENTS OF INJURY IN MUSCLE AND NERVE. 651 



This takes place only up to the next annular constriction, and after it has been 

 completed, the nerve under such conditions is devoid of current. A new trans- 

 verse section permits again of the development of a strong nerve-current. 



7. If the electrodes are applied to the two transverse sections of an 

 excised nerve or to two points on the surface equidistant from the 

 equator, a feeble current appears and passes in a direction opposite 

 to that caused by the physiological activity of the nerve-fiber (axial 

 current); therefore in the case of centrifugal nerves in a centripetal 

 direction and in that of centripetal nerves in a centrifugal direction. 

 Perhaps this current depends upon differences in the time of death at 

 the two extremities of the nerve. 



The electromotive force of such a current increases with the length of the 

 nerve-segment and with the size of the transverse section. It is enfeebled by ex- 

 haustion (by tetanization) , especially in the case of motor nerves and less in that 

 of centripetal nerves. 



The muscle-current can be demonstrated also without the aid of a multiplicator: 

 i. By a sensitive frog-preparation, designated the physiological rheoscope. A moist 

 conductor is applied to the transverse section and the surface of the gastrocnemius 

 muscle from a frog. When the sciatic nerve of a frog-preparation connected with 

 the leg is stretched over the muscle contraction takes place at once ; likewise when 

 the nerve is again removed. If at the lower extremity of the frog-preparation a 

 transverse section is made through the gastrocnemius muscle, and the sciatic 

 nerve (whose distribution in the muscle is connected with the surface of all of 

 the fibers) is placed on this transverse section, the leg twitches as the muscular 

 current, from the surface to the transverse section, enters the nerve. This obser- 

 vation was familiar to Galvani as contraction without metals. 



2 . An isolated muscle can be stimulated directly and made to contract by means 

 of its own muscle-current. If unpolarizable electrodes are applied to the transverse 

 section and the surface of a curarized frog-muscle and the circuit is closed by 

 mercury the muscle contracts. In an analogous manner the nerve also may be 

 stimulated by its own nerve-current. If the lower extremity of a muscle with a 

 transverse section be immersed in a 0.6 per cent, solution of sodium chlorid, which 

 itself is entirely indifferent, a secondary circuit is established through this fluid 

 between the transverse section and the adjacent surface of the muscle. In 

 consequence, the muscle contracts. Other indifferent conductors used to com- 

 plete the circuit have a similar effect. 



3. If the muscle-current be passed through potassium-iodid paste it causes by 

 electrolysis a separation of iodin at the positive pole, as a result of which the starch- 

 paste becomes blue. 



The total current in the body should be the resultant of the electrical currents of 

 the individual muscles and nerves, and, in the frog deprived of skin, it passes from the 

 extremity of the limbs to the trunk and in the trunk from the anus to the head. 

 This is the "corrente propria della rana" of Leopoldo Nobili, or the "frog-current." 

 In mammals the corresponding current passes in an opposite direction. 



If muscles or nerves have lost their irritability in the state of narcosis 

 induced by ether or chloroform, the muscle-current may persist and even be in- 

 creased. After death, the currents disappear earlier than the irritability. They 

 persist longer in the muscle than in the nerve, in which they are abolished earlier 

 in the more central portions. Also a motor nerve wholly paralyzed by curare 

 still exhibits the current (spark) , as did also a nerve in process of degeneration 

 that had lost its irritability entirely for two weeks. In the divided nerves of a 

 living animal the current-strength is at first increased after one or two days, while 

 later it diminishes. Muscles that have become rigid at times exhibit currents in 

 opposite directions in consequence of inequalities developed in the process of decom- 

 position. The nerve-current is reversed by boiling water or by desiccation. 



Of other tissues that exhibit electrical currents there may be mentioned the 

 skin (frog), whose surface is positive, while its inner aspect is negative. The 

 mucous membrane of the digestive tract exhibits the same relation, as does also 

 the cornea, as well as the aglandular skin of fish and snails. Currents have been 

 observed also in glands, principally in the unicellular and multicellular mucous 

 glands of lower vertebrates (frog, eel) . 



