THE FROG, AND ON THE ACTION OE THE VAGKTS NERVE. 
1011 
by a series of stimulations in each separate experiment, and, if so, what conditions are 
necessary for its production. 
In the first place, stimulation of the vagus is much more likely to reduce the force 
of the contractions down to complete quiescence immediately after removal of the heart 
from the body, than after it has been suspended for some time ; and, indeed, a variety 
of facts can be brought together which all point in one direction, viz.: that the produc¬ 
tion of quiescence by stimulation of the nerve stands in intimate relation with the 
existence of a suitable nutrition of the heart. Thus it frequently happens that typical 
inhibition can be obtained before the heart is removed from the body, although after 
it has been suspended it is impossible by any strength of stimulation to reduce the 
strength of the contractions to such an extent as to cause standstill. 
Again, experiments made in June for this express purpose show that if the heart be 
suspended as quickly after removal as possible, and the circulation be kept intact till 
the last moment, then, with a certain strength of current the first stimulation caused 
absolute quiescence ; the next, although of the same strength and length, only a primary 
diminution of the force of the contractions, and with succeeding stimulations of the 
same strength and the same length and following upon one another at as nearly as 
possible the same intervals of time, there was a decided tendency for the primary 
diminution of the contraction force not only to diminish in extent, but also to affect a 
smaller number of beats, until at last the stimulation caused an increase in the force of 
the contractions with a previous diminution of only one or two or even no beats at all 
(see Plate 68, fig. 9). 
Indeed, it can be said that in the course of each separate experiment the successive 
stimulations of the nerve tend to show the same gradation of effects from complete 
quiescence followed by augmentation on the one band, up to a simple primary augmenta¬ 
tion of the force of the contractions on the other, as has already been pointed out 
from the consideration of the whole number of curves. 
In the second place, the examination of my curves indicates that the nature of the 
special nutritive condition of the heart, upon which the phenomenon of vagus standstill 
depends, may possibly be given by the chemical examination of a large number of 
hearts at different times of the year, for as far as I can judge from this first series of 
experiments, standstill is more likely to occur upon vagus stimulation, after the heart 
has been cut out and suspended, in the early spring months of the year than in the 
summer months. Indeed, in some cases in March, stimulation was still able to cause 
quiescence even after the heart had remained suspended for nearly two hours. 
In Plate 68, fig. 12, curve A, I give an example of quiescence of the auricular contractions caused by 
vagus stimulation, which was obtained about an hour and a half after removal of the heart from the body, 
during which time the vagus had been stimulated nine times. In curve B of the same figure, which is a 
continuation of curve A (except that between A and B the vagus was stimulated so that the beats at the 
commencement of the curve B represent the maximum contractions due to that stimulation) the vagus 
was stimulated with the same strength, of current at frequent intervals, so that the auricle was not 
allowed to reach the maximum of its contractions. The curve shows well not only that quiescence was at 
first produced, but also the resolution of that quiescence into barely visible rhythmical contractions. 
