658 THEORIES OF CURRENTS IN MUSCLES AND NERVES. 



tendon may even become positive with respect to the surface. The parelectro- 

 nomic layer is destroyed by cauterization. 



The negative variation in current is explained by assuming that during the 

 activity of muscle and nerve the electromotive force of all of the molecules is di- 

 minished. On partial contraction of the muscle the contracted portion assumes 

 rather the character of an indifferent conductor, which is in simple conducting 

 connection with the negative zones of the resting contents of the muscular fibers. 

 The electrotonic currents beyond the poles, particularly in the nerve-fibers, require 

 a special explanation, while the electrotonic state of the muscles extends princi- 

 pally to the intrapolar portion. In explanation of the electrotonic currents, it 

 is assumed that the bipolar molecules have the property of rotation. The polar- 

 izing current, however, exerts a directive influence upon the molecules so that 

 these turn their negative surface toward the anode and their positive surface 

 toward the kathode. In consequence the molecules of the intrapolar segment are 

 arranged like the voltaic pile. In the portions of the nerve lying beyond the 

 pole the molecules are the less accurately arranged the farther removed they are. 

 Therefore, the deflections of the needle become correspondingly feebler in the 

 extra-polar portions. 



The differential theory proposed by Hermann, which has recently been de- 

 veloped by Hering, explains the phenomena in a satisfactory manner. Any proto- 

 plasmic structure, such as muscle, nerve, or cell, develops no current that can 

 be conducted outward so long as its metabolism, that is the internal chemical 

 processes, remains the same in all parts. Every disturbance of this equilibrium in 

 one part of the protoplasmic structure causes the development of currents that 

 can be conducted away. Therefore, (i) the protoplasm at the point where death 

 occurs, whether from injury of any kind or from degeneration, becomes electrically 

 negative with respect to living and irritable protoplasm. (2) The protoplasm is 

 negative at points that are irritated with respect to those that remain in an un- 

 irritated resting state. (3) The protoplasm becomes electrically positive in 

 warmed situations, negative in cooled situations. In addition it may be stated 

 (4) that protoplasm is strongly polarizable on its surface (nerve, muscle). The 

 constant of polarity is diminished by irritation (and death) . 



In detail the following statements may yet be made in this connection. It 

 has been shown that resting, uninjured and absolutely fresh muscles are entirely 

 without current, as also are wholly intact nerves. The heart likewise is free from 

 current, and also the muscles of fish still covered by skin. As the skin of the 

 frog possesses currents of its own, it is possible, with special precautions, after 

 destruction of the cutaneous currents through cauterants, to demonstrate also 

 here the freedom from current on the part of the frog's muscles. Furthermore, 

 L. Hermann found that the muscle-current always develops only after the lapse of 

 a certain, though short, time after making a transverse section. 



All injuries of muscles and nerves give rise at the site of injury (the demarca- 

 tion-surface) to negative, dying tissue with relation to the positive, intact tissue. 

 In this way is to be explained the negativity of the transverse section with relation 

 to the surface. The current thus developed is designated by Hermann the de- 

 marcation-current. If potassium-salts or muscle-juice be applied to certain parts 

 of a muscle these become electrically negative. If these substances are again 

 removed the negativity of these parts disappears. 



It appears to be a phenomenon peculiar to all living protoplasmic substances 

 that after injury at one point this becomes negative on dying, while the remaining 

 intact portion is electrically positive. Thus, all transverse sections of living 

 vegetable structures are negative with relation to their surface. The same con- 

 dition is observed in animal structures, for example glands and bones. The 

 electrical organ of fish is discussed on p. 675. 



Engelmann has made a remarkable observation. He found that the heart 

 and the unstriated muscle-fibers again lose the negativity of their transverse 

 section if the divided muscle-cells have died completely as far as the adjacent 

 cement-substance of the neighboring cells ; while nerves lose their negativity when 

 the divided segments, each corresponding to a single cell, have died to the nearest 

 annular constriction of Ranvier. Under such circumstances, all of these organs 

 are entirely without current, for the entirely dead substance reacts essentially as 

 an indifferent moist conductor. Also muscles divided subcutaneously likewise no 

 longer exhibit negative cut surfaces after union of the wound-surfaces. 



Notwithstanding all of the foregoing observations the preexistence of currents 

 in resting living tissues cannot be assumed. 



