140 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



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 needle 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. 



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 A but the 

 muscle of B will twitch (see Fig. 61). 

 If nerve A be excited by many 

 rapidly following induction shocks so 



FIG. 61. Secondary tetanus. ' 



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 be 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 

 the rapidly following excitations applied to A was the cause of a separate con- 

 traction process and a separate current of action in B the separate contractions 

 combined to produce the tetanus of B, but the separate currents of action did 

 not fuse, although they caused a continuous negative variation of the slowly 

 moving magnet of the galvanometer. 



The correctness of this view has been shown by experiments with the capil- 

 lary electrometer, which approaches the "physiological rheoscope," as the 

 nerve-muscle preparation is called, in its sensitiveness to rapid changes in elec- 

 trical potential. 



Burdon Sanderson 1 has obtained, by photographically recording the move- 

 ments of the column of mercury of the capillary electrometer (see Fig. 59, 

 p. 136), beautiful records of the changes of electric potential which occur when 

 an injured muscle is tetanized. 



The record in Figure 62 shows, first, a series of negative changes resulting 

 from the' separate stimuli. It is these which cause secondary tetanus and 

 which produced the negative variation current disclosed by the galvanometer 

 in the experiments of Du Bois-Reymond. Second, there is a more permanent 

 negative change, likewise opposed to and lessening the effect of the negative 



1 Journal of Physiology, 1895, vol. xviii. p. 717. 



