ACTION OF THE EXCISED MAMMALIAN HEART. 
241 
different cause ; whereas we regard the early monophasic variation as the expression 
of local predominance of a change taking place throughout the whole ventricle, we 
think that the late monophasic variation is in reality due to local activity at and near 
one of the two leading-off electrodes ; this, indeed, is often demonstrable at this period 
by local excitation, which then causes contraction restricted to definite spots. 
(6.) Excited contraction .—As regards the excitatory variation, our results with 
the electrometer were entirely similar to those which we have already described with 
the galvanometer. The accompanying Table summarises our electrometer observations. 
(Table K.) 
§ VIII. Conclusion. 
It would be superfluous to repeat, in summary, the facts relating to the mode of 
decline of the excised Mammalian heart which are described in the second, third, and 
fourth paragraphs of our paper. The extraordinary sluggishness of action, of which 
these showed us that the Mammalian heart is capable under the conditions of our 
experiments, tempted us to analyse as far as possible the mode and mechanism of 
cardiac contraction in Mammalia. 
In this direction the chief result, which we regard as established, is that on the 
Mammalian heart, under conditions similar to those in which the Frog’s heart has been 
examined in this respect, the passage of an excitatory wave is demonstrable as a 
diphasic variation with the galvanometer and the electrometer, and that the passage 
of a corresponding wave of contraction is demonstrable by mechanical methods. 
As regards the Mammalian heart, neither of these facts have, so far as is known to 
us, been hitherto observed ; as regards the Frog’s heart, we have incidentally added to 
the classical phenomenon of the diphasic variation a demonstration of its mechanical 
aspect as a wave of muscular contraction. The similarity between the excised 
Mammalian heart and the excised Batrachian heart is thus far complete. But there 
are points of divergence. Analysis of the spontaneous beat both by mechanical and 
by electrical methods brings these into evidence. The diphasic variation of the spon¬ 
taneously beating Frog’s heart is uniformly indicative of negativity of base, followed 
by negativity of apex ; to this we add the statement that muscular contraction of 
base precedes, and is followed by, muscular contraction of apex. All our experiments 
and measurements are thus confirmatory of the doctrine that the contraction takes 
place from base to apex, and that the wave of excitation and of contraction takes place 
by muscular channels. It is otherwise with regard to the Mammal heart. The variation 
is not always diphasic; immediately after excision it is more frequently monophasic 
and thereafter becomes diphasic. The movement of galvanometer and electrometer 
indicates for the monophasic variation negativity predominant either at apex or at 
base ; for the diphasic variation (when it is present) negativity of apex, followed by 
negativity of base, or the reverse. There is no constant rule, in fact, and we saw no 
use in further multiplying observations, seeing that we had to do with the irregulari- 
MDCCCLXXXVII.-B. 2 I 
