Electromotive Phenom. of the Mammal. Heart. 265 



a) It might travel in the muscular fibres. Tliis cannot he ac- 

 cepted without much stronger evidence. At present the bulk of evi- 

 dence seems to sliow that the wave of excitation in muscle is simul- 

 taneous, if not identical, with the wave of negativity. 



b) It might be conducted by a deeper layer of muscular tissue. 

 We think the following arguments tell against this view: 



1. The eifect of using cooled air in respiration must tend to 

 lower considerably the temperature of the blood pouring into the left 

 side of the heart. This will cool the internal layer of muscle so that 

 it will be in a worse condition for conducting excitation than the outer 

 layer which we are leading off. 



2. We made many attempts to lead oif two points on the inter- 

 nal smface of the left ventricle by means of non-polarizable electrodes 

 at the time when we were still using cold air in respiration, and hence 

 obtained apex negativity preceding basal negativity. The difficulties, 

 however, were so great that we only obtained one photograph presen- 

 ting a good diphasic variation, and this shews apex negativity prece- 

 ding basal negativity, (see Plate XV. Fig. 8), so disproving the sug- 

 gestion of a wave travelling internally from base to apex and then 

 externally from apex to base. The method used in leading off the in- 

 terior of the heart was the following. (Fig. 6.) 



The electrodes consisted of two narrow glass tubes, about three 

 inches long, curved for about half an inch at one end a and h. The 

 curvature of the basal electrode was more acute than that of the other. 

 These tubes were filled with saturated zinc sulphate solution; the cur- 

 ved ends were plugged with zinc sulphate clay, and just before use 

 a small plug of saline clay was pushed into the ends. An amalgama- 

 ted zinc wire was dipped into the solution and leakage was prevented 

 by a short bit of india-rubber tubing, connecting the zinc wii^e and the 

 glass tube; the copper wires soldered to the zinc were well insulated 

 by telegraph cement. Each of these tubes fitted into a block of ebo- 

 nite, one of which, viz: that for the apex c), had a spring attached 

 to it, armed with a button at its extremity and so arranged as to be 

 exactly opposite the end of the glass tube; the object of the spring 

 being to keep the electrode in contact with the ventricular wall. To 



