CH. XII.] 



THE RHEOTOME 



139 



(2, 2, 2, 2). The bar revolves, and by making or breaking the primary circuit sends 

 an induction shock into the nerve at the same instant. 



The muscle is connected by non-polarisable electrodes to the galvanometer ; 

 this circuit includes the brass blocks 2, 2, on the disc over which the bar revolves, 

 and a compensator not shown in the figure to neutralise any current set up by the 

 muscle in a state of rest. If an electrical change occurs in the muscle, it is only 

 noticed by the galvanometer if at the same time the bar on its revolution connects 

 the two brass blocks on the disc, and so completes the circuit. The apparatus can 

 be set so that the bar makes the primary contact (1, 1) simultaneously with the 

 galvanometer contacts, or that the galvanometer contact is made, 1, 2, 3, etc., 

 hundredths of a second later than the primary contact. If the two are closed 



FIG. 169. Scheme of a Rheotome. (Waller.) 



simultaneously the electrical condition of the muscle is tapped off at the moment of 

 excitation ; if the galvanometer contact is closed ^-5, yf^, ' T $ 7 , etc. second after 

 excitation, the electrical condition of the muscle at that particular instant is ascer- 

 tained. By a number of experiments with different intervals between the making 

 of the two contacts, one ascertains how long after the excitation the change in the 

 electrical condition of the muscle takes place. 



We can now pass on to a consideration of results. 



In muscles that are removed from the body, it is found that on 

 leading off two parts of their surface to a galvanometer, the galvano- 

 meter needle generally swings. The most marked result is obtained 

 with a piece of muscle in which the fibres run parallel to one another, 

 and the longitudinal surface is connected with one of the cut ends 

 by a wire (2 in fig. 170). 



On the course of the wire a galvanometer indicates that a current 

 flows from the centre to the cut end outside the muscle, and from 

 the cut end to the centre inside the muscle. If, now, the muscle is 



