96 THE CONTRACTILE TISSUES. 



the muscle A acts as a battery, the completion of the circuit of which by 

 means of the nerve of B serves as a stimulus, causing the muscle B to 

 contract. 



If, while the nerve of B is still in contact with the muscle of A, the 

 nerve of the latter is tetanized with an interrupted current, not only is the 

 muscle of A thrown into tetanus, but also that of B, the reason being as 

 follows : At each spasm of which the tetanus of A is made up, there is a 

 negative variation of the muscle-current of A. Each negative variation of 

 the muscle-current of A serves as a stimulus to the nerve of B, and is hence 

 the cause of a spasm in the muscle of B ; and the stimuli following each 

 other rapidly, as being produced by the tetanus of A they must do, the 

 spasms in B to which they give rise are also fused into a tetanus in B. B, 

 in fact, contracts in harmony with A. This experiment shows that the 

 negative variation accompanying the tetanus of a muscle, though it causes 

 only a single swing of the galvanometer, is really made up of a series of 

 negative variations, each single negative variation corresponding to the 

 single spasms of which the tetanus is made up. 



But an electrical change may be manifested even in cases when no cur- 

 rents of rest exist. We have stated ( 66) that the surface of the uninjured 

 inactive ventricle of the frog's heart is isoelectric, no currents being observed 

 when the electrodes of a galvanometer are placed on two points of the sur- 

 face. Nevertheless, a most distinct current is developed whenever the 

 ventricle contracts. This may be shown either by the galvanometer or by 

 the rheoscopic frog. If the nerve of an irritable muscle-nerve preparation 

 be laid over a pulsating ventricle, each beat is responded to by a twitch of 

 the muscle of the preparation. In the case of ordinary muscles, too, 

 instances occur in which it seems impossible to regard the electrical change 

 manifested during the contraction as the mere diminution of a pre-existing 

 current. 



Accordingly, those who deny the existence of " natural " muscle-currents 

 speak of a muscle as developing during a contraction a "current of action," 

 occasioned, as they believe, by the muscular substance as it is entering into 

 the state of contraction becoming negative toward the muscular substance 



which is still at rest, or has returned to a 



FJG 31 state of rest. In fact, they regard the 



negativity of muscular substance as cha- 

 racteristic alike of beginning death and of a 

 beginning contraction. So that, in muscu- 

 lar contraction a wave of negativity, start- 

 ing from the end-plate when indirect, or 

 from the point stimulated when direct 

 stimulation is used, passes along the mus- 

 cular substance to the ends or end of the 

 fibre. 



For instance, we will suppose two elec- 

 trodes placed on two points (Fig. 31), A 

 and B, of a fibre about to be stimulated by 

 a single induction-shock at one end. Before 

 the stimulation the fibre is isoelectric, and 

 the needle of the galvanometer stands at zero. At a certain time after the 

 shock has been sent through the stimulating electrodes O), as the wave of 

 contraction is travelling down the fibre, the section of the fibre beneath A 

 will become negative toward the rest of the fibre, and so negative toward 

 the portion of the fibre under i.e., A will be negative relatively to B, 

 and this will be shown by a deflection of the needle. A little later B will 



