CONNECTED WITH THE BEAT OF THE MAMMALIAN HEABT. 
173 
taneity of action throughout a contractile mass, l)ut tliat it may depend u]jon 
unbalanced, and therefore predominant, negativity of a less injured and literally 
“ stronger” portion of tissue, is very clearly shown with a strip cut from a fresh ven¬ 
tricle. It is not difficult in this case to combine mechanical with electrical exploration. 
Two levers resting upon the ventricle-strip record the passage of the wave of contrac¬ 
tion, and the strip is at the same time led off from each end to the electrometer. A 
stimulus is applied to one end, the contraction passing along the strip is recorded by 
the two levers, and the electrical variation is watched in the electrometer. Usually 
the strip will be found not to contract equally strongly in its whole length, but one 
end gives a stronger contraction than the other. With this inequality of contraction 
a concordant inequality of electrical action is observed ; the variation is not diphasic, 
but monophasic, indicating a predominant negativity of the more strongly contracting 
part, while by the asynchronism of the two levers we obtain ocular evidence of the 
passage of a wave of contraction. Sometimes the effect is the same whether the 
contraction be started from the stronger or from the weaker end ; only in the first case 
the single phase is an intensified first phase, in the second case it is an intensified 
second phase. Sometimes it happens that the inequality of tissue is of such a degree 
that by excitation started at the “ strong ” end of the strip a monophasic variation is 
obtained, while by excitation at the “ weak ” end a diphasic variation is obtained, 
consisting of a minor first phase (negativity of the weak end), followed by a major 
second phase (negativity of the strong end). 
Fig. 2. 
Excitation of A gives Variation S (predominant 1st phase). 
,, B ,, ,, S (predomiirant 2nd phase) ; 
or ??S (minor 1st phase ; major 2nd phase). 
The phenomena observed on the excised isolated auricle are of a similar character. 
Adopting the disposition above described, we may witness the passage of a wave of 
mechanical contraction attended by a monophasic variation, due to injury of its 
ventricular portion and consequent unbalanced negativity of the appendicular end. 
What is the order of occurrence of the two phases ? 
Examination of the uninjured heart m situ shows that in the majority of cases it 
