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AN AMERICA X TEXT-BOOK OF PHYSIOLOGY. 



its own current, provided the longitudinal and fresh cross section were 

 united suddenly by a good conductor. 



3. Currents of Action in Muscle. — Just as the dying tissue of nerves 

 and muscles is electrically negative as compared with normal tissue, so active 

 nerve- and muscle-tissue is electrically negative as compared with resting 

 tissue. 



Du Bois-Reymond discovered that if the normal longitudinal surface and 

 injured cut end of a muscle were connected with a galvanometer and the muscle 

 were tetanized, the magnet swung hack in the opposite direction to the deflec- 

 tion which it had received from the current of rest. This backward swing of 

 the magnet was not due to a lessening of the current of rest, for if the effect 

 of the current of rest on the galvanometer were compensated for by a battery 

 current of equal strength and of opposite direction, so that the needle stood at 

 0, and the muscle were then tetanized, there was a deviation of the needle 

 in the opposite direction to that given it by the current of rest, Du Bois- 

 Reymond called this current of action the negative variation current. This 

 negative variation current was found to last as long as the muscle continued in 

 tetanus. On the cessation of the stimulus the current subsided more or less 

 rapidly and the ueedle returned more or less completely to the position given it 

 by the current of rest before the excitation. The return was rarely complete, 

 and by repeated excitations there was a gradual lessening of the current of 

 rest, the amount varying with the extent of the preceding irritation. The 

 strength of the current of action is influenced greatly by the condition of the 

 muscle, the temperature, etc. It increases with increasing strength of 

 excitation, in the same way as the strength of the contraction. 1 



Secondary Tetanus. — Matteucci and Du Bois-Reymond (1842) both dis- 

 covered the phenomenon which Du Bois-Reymond called secondary tetanus. 



If two nerve-muscle preparations be 

 made, and the nerve of preparation B 

 be laid on the muscle of preparation 

 A, when the nerve of A is stimulated, 

 not only the muscle of .1 but the 

 muscle of B will twitch (see Fig. 65). 

 If nerve A be excited by many 

 rapidly following induction shocks so 

 that muscle A enters into tetanus, 

 muscle B will also be tetanized. The phenomenon is not due to a spread of 

 the irritating electric current through nerve and muscle A to nerve B, for the 

 tetanus of both muscles stops if nerve A lie ligated ; moreover, a secondary 

 tetanus is obtained in case tetanus of muscle A is called out by mechanical 

 stimuli, such as a series of rapid light blows, applied to nerve A. 



Du Bois-Reymond considered '"secondary tetanus" a proof of the discon- 

 tinuity of the apparently continuous contraction of tetanus, for muscle B could 

 only have been excited to tetanus by rhythmic excitations from A. Each of 

 1 Burdon-Sanderson : Journal of Physiology, 1898, xxiii. p. 323. 





Fig. 65. — Secondary tetanus 



