432 



THE FUNCTIONS OF CROSS-STRIATED MUSCLES 



portions, say b l to c lf c^ to d lt d^ to e w etc., of course it will be possible to obtain 

 the form of the entire variation. An apparatus which would enable us to make 

 such determinations must permit of connection with the galvanometer at a 

 definite moment after the beginning of the variation, and of breaking this con- 

 nection at any desired moment during the variation. Since the electrical varia- 

 tion in muscles and nerves is started by the excitation, the requirements will be 

 met if the galvanometer circuit can be closed or broken at any given interval 

 after the instant of stimulation. 



The rheotome of Bernstein (Fig. 169) consists of a wheel (r) revolving about 

 a vertical axis, and carrying on its circumference three rnetal pegs, one of 

 which (c) gives the stimulus to the nerve by closing or opening the primary 

 current to an induction coil ; the other two pegs insulated from the first, but 

 in electrical connection with each other, serve to close and open the galvanometer 

 circuit. At each revolution of the wheel the pegs c l and c, dip into the mercury 

 troughs (q, and # 2 ) respectively which are connected with the muscle on the one 



hand and the galvanometer on 

 the other. The mercury troughs 

 are movable with respect to 

 each other, so that the dura- 

 tion of the galvanometer cur- 

 rent can be varied within wide 

 limits. If now the wheel is re- 

 volved at a certain speed, with 

 each revolution the muscle will 

 receive a stimulus and the gal- 

 vanometer circuit will be closed 

 for a certain definite time after 

 each stimulus. If we have the 

 two contacts so arranged that 

 the galvanometer is connected 

 with the muscle at the same 

 instant that the stimulus is 

 given, the excursion of the 

 galvanometer will represent 

 the first part of the variation 

 evoked by the stimulus. Then 



by shifting the contacts, the galvanometer can be connected at different inter- 

 vals following the instant of stimulation until the entire variation is recorded. 



If a muscle (or the heart) or a nerve be connected at two uninjured 

 places (a and b, Fig. 170) with a galvanometer, and it be then stimulated 

 at some outside point (c), the galvanometer shows that the point a situated 

 nearer the point of stimulation becomes electrically negative to &, and then 

 the current is reversed and b becomes negative to a (cf. pages 48 and 179). 

 The action current therefore consists of two phases, each of which gives ex- 

 pression to the general law, that every active point of a muscle or nerve is 

 electrically negative to every resting point (page 48). When the excitation 

 spreads from the point c, the nearer of the two points naturally becomes 

 active first, while the more distant point (b) is still resting; hence the 

 first phase. When the excitation reaches the point b and the point a first 

 stimulated has gradually passed into a resting state, the second phase 

 appears. 



FIG. 169. Rheotome of Bernstein. 



