8 SIR THOMAS LEWIS 



between the two methods of leading off should not influence the direction 

 of the first potential difference exhibited by contact C and Z, when, as 

 in our illustration, we are dealing with a straight and narrow strip of 

 muscle lying in one line between the contacts ; but as we shall see, it 

 becomes of consequence when the relation of muscle to contacts is 

 altered. A second difference between the two methods of leading off is 

 also to be noted. When, in the last experiment, the muscle is embedded 

 in a conducting substance, the current flows not only through the muscle 

 and galvanometer ; it flows through the surrounding medium. In other 

 words, we have introduced a series of shunts along the borders of the 

 muscle and these decrease the amount of current flowing through the 

 galvanometer. While we may expect the movement of the galvano- 

 metric recorder to maintain its original direction (contact Z showing 

 relative negativity to contact C), we may not expect its movement to be 

 so considerable. 



I emphasize the fact that the comparison made is between an actual 

 experiment (Fig. 1 A) and a theoretical experiment (Fig. IB). The 

 actual events in the second experiment (Fig. IB) have, I think, not been 

 recorded, though there is sufficient evidence based on observation of a 

 less direct kind to convince us that the curves obtained in the first and 

 second experiment will have the same general form in their initial phase. 

 That there will be this smilarity is, I think, generally recognized ; it is 

 not a matter in dispute. But this conception is apt to lead up to a 

 second, namely, that curves taken by the two methods are built up in 

 identical fashions ; and that the two methods of leading will in all 

 circumstances yield similar results. They may do so when a simple and 

 narrow strip of muscle is placed in line with the leading off contacts; 

 but they do not, I believe, in all circumstances. Suppose that the 

 unembedded muscle is bent on itself at one end and that the contacts are 

 placed at 2 and 3 (Fig. 1C). Again, there will be agreement as to the 

 effect produced. Soon after 1 is stimulated, a current will flow through 

 the galvanometer in the original direction, indicating that contact Z 

 has become relatively negative to C, This change is set up when the 

 muscle on which contact Z lies becomes active. It is not produced by 

 activity of the muscle strip between 1 and 2 ; activity in this portion of 

 the muscle has no material effect since the free end 1 is not connected 

 to the leading off contact C. This illustration serves to emphasize 

 the fact that when contacts are placed directly on the muscle, that it is 

 an event occurring in the muscle immediately under the proximal con- 

 tact which is responsible for the first swing of the recording instrument. 



We come next to the fourth and crucial example, the muscle bent on 

 itself and embedded (Fig. ID). In these circumstances how will the 

 current first flow? I have asked this question of many physiologists 



