192 
DR. A. D. WALLER ON THE ELECTROMOTIVE CHANGES 
Postscript. 
(Added February 7, 1889.) 
The observations recorded in Part I., § 3, can be carried out on Animals at liberty. I 
have done so on Dogs and on a Horse, with the result that any two anterior or posterior 
extremities constitute an “unfavourable lead-off,” and that any one anterior in con¬ 
junction with any one posterior extremity forms a “favourable” combination. For 
purposes of demonstration I give the observations the following form :—A large Dog, 
trained to stand still with his feet in vessels of salt solution, is made to do so with a 
favourable and an unfavourable pair of extremities in connection with the electrometer, 
a commutator being interposed so that either pair can be switched on to the electro¬ 
meter without delay or disturbance. The mercury pulsates distinctly or not at all 
according as connection is made with a favourable or with an unfavourable combination. 
To the observations recorded in Part IT. I have added the following :—If two 
persons are connected with the electrometer as shown in fig. 9, their contracting 
hearts form battery when they are synchronous, and the normal variations are seen 
reinforced in degree; when, on the other hand, the two hearts are alternating in 
action there is interference of their electrical variations ; during this interference the 
movement of the mercury may be quite illegible, or the rhythm of each heart may 
be separately legible by following their separate pulses, the event depending upon 
the rates at which the two hearts are beating. 
Fig. 9. 
