THE FROG, AND ON THE ACTION OF THE VAGUS NERVE. 
1029 
As a conceivable Hypothesis, then, it seems to me we may say—the vagus increases 
the activity of the formative processes going on in the muscle, and it will produce 
therefore augmentation of the force of the contractions alone, or diminution followed 
by augmentation, or even standstill followed by augmentation, according as that 
activity is more or less equally distributed over the different stages of the process, the 
ultimate end of which is the formation of the final contractile substance. 
Again, although I am not prepared at present to offer any definite theory to explain 
the action of the nerve upon the motor ganglia, yet still it is impossible to help being 
struck with the apparent resemblances between its action on these cells and on the 
muscle cells; thus just as in the case of the muscle the nerve may at one time cause 
diminution followed by augmentation of the contractions, at another time augmenta¬ 
tion alone without any previous diminution, so in the case of the motor nerve cells, 
the vagus may under certain conditions cause a slowing of the rate of discharge of the 
impulses followed by acceleration, under other conditions acceleration alone without 
any previous slowing. 
I venture, therefore, to suggest that— 
The vagus is the trophic nerve of both the muscular tissue and the motor ganglia, 
meaning thereby that it increases the activity of the various formative pro¬ 
cesses going on in both these kinds of tissue, and it produces all its effects 
by virtue of this quality. 
In all that I have hitherto said I have been speaking entirely of the hearts of Frogs 
and Toads, and so far as these animals are concerned I venture to think that my views 
are in harmony with an experiment of Foster and Dew-Smith,* * * § who showed that 
although the constant current was able to cause rhythmical contractions in the isolated 
and quiescent apex or ventricle, or in the whole heart when rendered quiescent by the 
Stannius ligature, yet it was unable to do so when the heart was reduced to standstill 
by the stimulation of the vagus. This remarkable experiment, which, as far as I know, 
has never been disputed or explained, seems to me to follow naturally from the experi¬ 
ments and conclusions put forward in this paper. 
As yet I have not made any experiments upon the hearts of warm-blooded animals, 
and cannot therefore assert from my own observations that the vagus acts in a similar 
way upon them ; there are, however, certain experiments recorded which render this 
conclusion more or less probable. Thus Panum and GianuzziI have both observed 
that in Rabbits with weakl y-beating hearts, stimulation of the vagus causes the beats 
to become much stronger. TeatjbeJ has observed that in a curarised animal the heart 
beats for a longer time after the cessation of artificial respiration with the vagi intact 
than when these nerves have been previously cut; and Brown-Seqtlard§ has quite 
* Journ. Anat. and Physiol., vol. x. 
f Hermann’s Handbuch der Phyiol., Bd. iy., S. 384. 
f Allgem. Med. Centralzeitung, 1864, N. 42. 
§ Gaz. Med. de Paris, 1880, p. 391. 
