424 



THE PROPERTIES OF STRIPED MUSCLE. 



needle to come to rest depends on instrumental, not on physiological, 

 conditions, it has no special interest. 



When the capillary electrometer is used, a toothed curve is obtained 

 (uninjured sartorius), which brings to mind the ideal representation of 

 the " negative variation " in tetanus given by du Bois-Eeymond. In 

 the photographic curve shown in Fig. 237, obtained from the injured 

 sartorius, it is easy to distinguish the general or integral form on which 

 the humps are inscribed, each corresponding to the description given 

 of a single monophasic variation (Fig. 232). If the frequency of excita- 

 tion be about 30 per second, the starting-point of each individual curve 

 of the series will coincide with the very beginning of tbe decline of the 



Fig. 237. — Tetanus curve of injured sartorius. 



preceding one. The form of the integral curve is such as to show 

 that the electrical change which takes place at the beginning of a 

 tetanus is a sudden one. This is proved by the following experiment : — 



The apparatus is so arranged that immediately the advancing edge of the 

 plate passes behind the slit, the tetanising induction currents begin to act. The 

 excursion in the electrometer is photographed, and a comparison curve is 

 then made in the way already described, by introducing at a given moment a 

 known difference of potential with the same muscle in circuit. The general 

 form of this comparison curve is the same as that produced by excitation, 

 with the exception that the comparison curve has of course no inequalities. 

 What we learn from this correspondence is that in each case the difference of 

 potential attains its eventual amount at once. 



If an uninjured muscle, with the contacts arranged in a similar way, 

 is observed, it may happen that the meniscus remains nearly at the 



same height throughout 

 the period of tetanic 

 excitation. In this case 

 the integral curve is 

 nearly parallel to the 

 zero line. The spikes 

 which represent the suc- 

 cessive excitations pro- 

 ject upwards from the 

 curve, each having the 

 form of a normal 

 diphasic response to a single instantaneous stimulation (Fig. 238). 



The writer 1 has shown that other forms of continuous contraction, 

 evoked either by a single instantaneous stimulation, or otherwise, are 

 accompanied by electrical changes which, while they resemble in general 



1 Loc. tit., ii. 142. 



Fir,. 238. — Responses to ten excitations of an uninjured 

 gastrocnemius. Frequency about 40 per second. 



