272 ANIMAL PHYSIOLOGY. 
the cardiac beat or augmentation of its force, or to both, as is 
commonly the case. In every instance the work of the heart 
is increased, so that they may be called more appropriately 
augmentor nerves; and their effect may be more evident. on 
one part of the heart, as regards increase of the force of the 
beat, than on another. . 
They require for their fullest effect a rather strong and con- 
tinuous stimulation (interrupted current), and the augmenta- 
tion outlasts the stimulus a considerable period. The same law 
applies to them as to the vagus nerve, viz., that the result is 
inversely proportional to the rhythm of the heart at the period 
of stimulation; a slow-beating heart will be more augmented 
proportionally than a rapidly-pulsating organ. 
It is noticeable that after one or more experiments the heart 
often falls into an irregular or weakened action quite the re- 
verse of what ensues when the vagus is stimulated. But it has 
also been observed that certain of the vagus fibers on stimula- 
tion give rise to a like result. 
Further, it is found that the electrical condition of the heart 
is different, according as the inhibitory or other fibers of the 
heart are stimulated. The latter fact seemed to point strongly 
to a fundamental difference in their effect on cardiac metabo- 
lism; hence it is proposed to speak of the vagus as a vago- 
sympathetic nerve, containing inhibitory fibers proper and 
sympathetic or motor fibers to be classed with the nerves that 
were formerly known as “accelerators,” and to be compared 
in their action to the ordinary motor nerves of voluntary 
muscles. 
Indeed, these conceptions will probably give rise to a broader 
view of the whole nervous system, especially as regards the 
relations of the nerves themselves. 
Certainly the augmentor nerves to which we are now refer- 
ring exhaust the heart, lead it to expend its nutritive capital, 
and leave it worse than before. One can understand the ad- 
vantage in the heart having a double supply of nerve-fibers 
with opposite action; and it is worthy of special note in this 
connection that, when the vagus (vago-sympathetic) is stimu- 
lated at the same time as the augmentors, the inhibitory effect, 
preservative of nutritive resources, prevails. 
It will be seen that the heart may be made to do increased 
work in three ways: Firstly, the relaxation of a normal inhibi- 
tory control through the vagus nerve by the cardio-inhibitory 
center; secondly, through the sympathetic (motor) fibers in 
