422 



THE PROPERTIES OF STRIPED MUSCIE. 



with Professor Gotch. 1 The sartorius muscle is connected with the galvano- 

 meter circuit, which is arranged as in Fig. 223. The nerve is excited hy a 

 rheotome, the galvanometer wires of which go to K 4 . This also closes the 

 galvanometer circuit automatically at any desired time after excitation. 

 The "closing time" of the rheotome is very short — usually 5-^ second, it 

 having been found that the greatest (negative) deflection is obtained when 

 the closure begins about 0"006 second after excitation. The slider of the 

 compensator is so adjusted that the derived current is in the opposite direction, 

 and of just sufficient strength to annul the deflection when the excitation is 

 repeated. In the gastrocnemius the mean difference of potential in five 

 series of observations was found to be 0"084 volt. 



(b) The electrical response to a series of stimulations. — The nature 

 of the change which accompanies tetanus, when observed in an injured 

 muscle, with leading-off contacts on the natural and cross sections 

 respectively, was investigated by du Bois-Reymond some fifty years 

 ago. 2 He interpreted the imperfect data which the methods then avail- 

 able afforded, with wonderful sagacity — drawing therefrom inferences 

 which were surprisingly near the truth. It was more than twenty years 

 later 3 that, with the aid of the much better instruments which 

 his own ingenuity and the progress of science had placed in his hands, 



he published an 

 account of the 

 phenomena to 

 which he applied 

 the term " nega- 

 tive variation." 

 His general view 

 of what happens 

 in tetanus can be 

 best understood 

 by referring to 



the curves by which he represents it, as reproduced in Fig. 235. 

 The broken line is the curve of what he calls the Gesammtschwankung \ 

 the integral curve of the " variation." The successive effects of which 

 it is supposed to be made up are represented by the teeth of the 

 "ctenoid curve," the relation of which to the integral curve is such 

 that, if as many equidistant ordinates were drawn to the latter as 

 there are teeth, the space enclosed between the horizontal line ah, 

 the curve, and any two neighbouring ordinates, would represent the 

 integral of the differences of potential existing between the contacts 

 during the corresponding period. Each tooth, therefore, represents 

 the response to a single instantaneous excitation. The figure further 

 denotes that tetanisation is followed by an "after-effect" — a slight 

 diminution of the previous difference of potential. 



The " negative variation " of uninjured muscle was also investigated 

 by du Bois-Reymond in the same exhaustive way, particularly that of 

 the gastrocnemius, and he represented his conception of it graphically. 

 He found that, even when there was previously no difference of potential 

 between the contacts, the proximal contact became negative during 



1 See "Proc. Physiol. Soc," Joum. Physiol., Cambridge and London, 1891, vol. xii. p. 43. 



2 du Bois-Reymond, " TJntersuch. ueber thierische Electricitiit, " 1894, Bd. ii. S. 91, 

 Fig. 89. 



3 du Bois-Reymond, "Gesammelte Abhandlungen," Bd. ii. S. 559. 



Fig. 235. — After du Bois-Reymond. 



