232 
DR. A. D. WALLER AND MR. E. W. REID ON THE 
§ VI. Galvanometer Indications. 
It is necessary first to describe the plan of our apparatus, and the meaning of the 
abbreviations we shall have to use. 
The heart, having been excised, was laid upon an insulating support, slightly hollowed 
to receive it, and the ventricle, right or left, led off by unpolarisible electrodes applied 
near base and near apex respectively. The disposition adopted was such that the 
apex was always in connection with the north screw of the galvanometer, the base 
being in connection with the south screw ; we call these points respectively A and B. 
Current through the galvanometer from A to B is indicated by a deflection south of 
the magnet, current from B to A by a north deflection : it is thus apparent that a 
north deflection indicates that A becomes negative to B; that a south deflection 
indicates that B becomes negative to A. To denote the deflections north and south 
respectively, we use the letters N and S for large deflections, n and s for small deflec¬ 
tions. We used a very delicate Thompson galvanometer (Pi = 13,000 ohms); the 
periodicity of its oscillations was such as not to allow us to make observations at 
intervals of less than half a minute. 
This was in some cases a disadvantage ; it was, however, soon apparent to us that 
the condition of the heart itself is generally such as to forbid the too frequent 
repetition of excitations. 
In observations of the kind which we had to make it would have been useless to 
take exact measurements in number of degrees, and we contented ourselves with the 
occasional use of the qualifications “ large ” and “small” to express the relationship 
to each other of the two phases of the diphasic variation which usually came under 
our observation. 
Any electrical inequality between the two led-off points was compensated in the 
usual manner by means of a Sanderson’s potentiometer ; we used the same instru¬ 
ment to take measurements of such differences of potential. 
Our observations by the galvanometer are in the main confirmatory for the 
Mammalian heart of the fundamental facts established on the Frog’s heart by the 
researches of Engelmann, Burdon Sanderson, Marchand, and others, but with 
certain reservations and amid frequent irregularities, owing to the presumably more 
mobile nature of the Mammalian organ. We know 7 already, from the observations of 
