CONNECTED WITH THE BEAT OF THE MAMMALIAN HEART. 
177 
marked by a mouophasic and only a few by a diphasic variation, which, as time goes 
on, becomes gradually more frequent until it is established as the regular accompani¬ 
ment to every beat. 
Effects of double injury.-^As stated above, the conversion of a diphasic into a 
monophasic variation can be effected at will by injury, and T have just said that the 
monophasic variation thus effected may gradually give place to a diphasic variation ; 
it rem.ains to add that this may sometimes be done at once by a second injury. Thus, 
for instance, in a heart giving a spontaneous variation SN (apex negative, base 
negative), this was replaced by a variation N (unbalanced negativity of base) after 
injury of apex, and this again was at once replaced by a variation SN after a subse¬ 
quent injury of the base {vide Experiment 2 ). Apparently, the balance between the 
two led-off parts can be at least partially restored when, after one part has been 
injured, the second is similarly injured. 
A triphasic ventricular variation .—The ventricular variation sometimes appears 
to be triphasic, and one might at first sight interpret it as being due to auricular 
negativity followed by the ordinary diphasic variation. This, doubtless, does 
frequently give a variation of such a character, but in certain cases a treble variation 
is undoubtedly caused by the ventricle alone. A variation wSN (apex to H 0 SO 4 ; 
base to Hg) or sNS (apex to Hg ; base to HgSO^) cannot be auriculo-ventricular, 
but must be an irregularity such that negativity of the apex manifests itself twice, 
once at the beginning and once at the end of the contraction of the ventricles. The 
most probable interpretation appears to me to be that we have to do here with a case 
of injured base; apex negativity manifests itself first and is not overcome by subse¬ 
quent base negativity, which is only sufficient to more or less interrupt the predominant 
apex negativity; the latter thus appears to be twice manifested. The following 
photographic observation is one among several others which can, it seems to me, be 
thus explained. 
Plioto. 1. 
Ba: Kx Sp 
Experiment 4.— Kitten’s heart, excised 15 min. post mortem, A.pril 13, 1 888 . 
Apex to Hg. Base to H, 2 S 04 . 
= a spontaneous variation 
Ax = a variation caused by mechanical excitation of the apex, 
Bx = a variation caused by mechanical excitation of the base, nS. 
2 A 
MDCCCLXXXTX.—B. 
