ELECTRO-PHYSIOLOGY 



723 



perfected a method for the measurement of the curves, the differential 

 rheotome, originally constructed by Bernstein, was the most valuable 

 instrument we possessed for experiments on the time relations of 

 these phenomena. By its aid, for instance, it was shown that the rate 

 of propagation of the electrical change in muscle is the same as 

 that of the mechanical change, and in nerve the same as that of the 

 nervous impulse. Observations on muscle made by the capillary 

 electrometer and the string galvanometer have confirmed those 

 results. The velocity of propagation of the diphasic variation along 

 a fresh sartorius at 14 C. was in one experiment 2'8 metres, in 

 another at 18 C. s 3^5 metres (Sanderson). (See p. 659.) Lucas 

 has pointed out that in strict accuracy what is observed is merely 

 that the time interval separating contraction at one point of the 

 muscle from contraction at another is equal to the time interval 

 separating the electrical changes which occur at the same points. The 

 facts observed do not formally prove that either the contraction or the 

 electrical disturbance is pro- 

 pagated at all. So far as they 

 go, some other perfectly dis- 

 tinct change may be pro- 

 pagated, which at all points 

 of the fibre at which it arrives 

 sets up both the contraction 

 and the electrical change. 

 Such direct evidence,however, 

 as we possess goes to show 

 that it is the electrical disturb- 

 ance which is the propagated 

 one, and that this evokes the 

 contractile disturbance. 



The differential rheotome 

 (Fig. 275) consists essentially 

 of a stationary metal ring, 

 the whole or part of which is 

 graduated, and of a portion 

 which can be made to revolve 

 at a known rate. The latter 

 carries two contacts : a, an 

 obliquely - placed platinum 

 wire which touches at every 

 revolution a horizontal wire b 

 on the fixed ring, thus making and breaking the primary circuit P 

 of an induction machine, and so causing stimulation of a muscle 

 or nerve M connected with the secondary^'S ; and, c, a double 

 contact, either in the form of two platinum wires, which dip into 

 two mercury troughs, or of two wire brushes rubbing on copper 

 blocks d, at a certain part of the revolution. The troughs or 

 blocks are connected with a circuit containing a galvanometer G, 

 and a portion of the muscle or nerve arranged so as to give a 

 strong action current. This circuit is completed by the wires or 

 brushes, which are in metallic contact with each other ; and the 

 relative position of the fixed contact in the primary circuit and 

 of the troughs or copper blocks can be altered so as to alter at will 

 the interval between stimulation and closure of the galvanometer 

 circuit. The proportion of the whole revolution during which this 

 circuit is closed can be varied by changing the relative position of 



462 



FIG. 275. DIAGRAM OF DIFFERENTIAL 

 RHEOTOME. 



