THE EUNCEIONS OF THE VISCERAL NERVES 93 
J 
the vagus increases the heart’s action, while a slightly stronger application 
diminishes the frequency and force of its contractions. This conclusion is in 
harmony with an observation which I made incidentally upwards of a year 
ago, that irritation of the posterior part of the brain of a frog with a fine needle 
was repeatedly followed by improvement in the circulation, whereas it was 
by the application of a stronger stimulus, that of galvanism, to the same 
part of the cerebro-spinal axis that Weber first induced an inhibitory action 
on the heart. 
It is said, on apparently good authority,’ that division of the vagus in 
mammialia is invariably followed by increase of the action of the heart ; this, 
if true, would be a strong ground for believing in an inhibiting influence con- 
stantly operating upon it through this nerve. But it is also stated that the 
same thing does not occur in frogs ; and this circumstance appeared to me to 
throw much doubt upon the evidence regarding mammalia. I therefore made 
careful experiments on the effects of cutting both vagi, once upon a calf and 
four times upon rabbits, taking the number of the heart’s beats immediately 
before and immediately after section of each nerve by the momentary stroke 
of a sharp pair of scissors. In no case was the rate increased at all by the 
operation, and the very gradual diminution in frequency that commonly took 
place appeared to depend on general exhaustion from other circumstances 
attending the experiment. In one rabbit, in which I had removed the skin 
and pectoralis major from the praecordial region, so as to see the movements 
of the heart distinctly through the transparent pericardium and _ intercostal 
muscles, I noticed particularly that the strength of the contractions, as well as 
their frequency, remained quite unaffected by the division of the vagi. From 
these facts I feel warranted in concluding that, whatever may occur under 
exceptional circumstances, there is certainly no constant control exercised 
over the heart’s action through those nerves. 
The influence of the spinal system upon the heart is, however, very apparent 
after a struggle, which almost invariably increases the frequency and force of 
the beats; and I found that this continued to be the case after division of both 
vagi, implying that those nerves are not the only channels through which this 
influence is transmitted. A new field of investigation was thus opened. For, 
supposing the inhibitory agency to be simply the greater action of an ordinary 
nerve, it would probably not be exercised exclusively by the vagus, but also 
by the other nerves connecting the cerebro-spinal axis with the cardiac ganglia, 
viz. the sympathetic branches in the neck ; in which case the action of the heart 
should be increased or diminished, according to the strength of the stimulus, 
= Pileer,-op. cit. 
