A CTION OF THE A UG MENTOR NER FES. 2 1 7 



of the augmentor most conspicuous later. I have chiefly studied the 

 influence of the augmentor nerve upon conduction in the heart of the 

 frog and toad, by means of the clamp in the auriculo-ventricular 

 groove. When the clamp is tightened so that a partial block is caused, 

 and the ventricle is responding to every second or more contraction of 

 the auricle, then stimulation of the augmentor nerve forces the block, so 

 that every contraction passes, even although the rate is increased by the 

 stimulation. The same action upon the passage of a contraction wave 

 over a block, as the result of stimulation of the augmentor nerve, has 

 been described by MacWilliam for the eel, and by Bayliss and Starling l 

 for the mammalian heart. 



The position of the augmentor nerves seems clear. They belong, as 

 already mentioned, to the same great group of visceral nerves as the 

 vaso-constrictors ; they increase the rhythmical power of that part of the 

 heart which is initiating the rhythm ; they increase the contraction force 

 and conductivity of the cardiac muscle. They may distinctly be con- 

 sidered as the cardio-motor nerves, the difference between them and other 

 motor nerves being due to the fact that they are motor to a rhythmical 

 instead of a quiescent muscle. The question then arises, Can such a 

 motor nerve cause a quiescent heart to beat ? At first sight it would 

 appear that the answer to this question must be in the affirmative, for as 

 long ago as 1860, Schelske 2 asserted that the vagus, i.e. the conjoint 

 vagus and augmentor nerves, could make the frog's heart beat again 

 when it was reduced to standstill by raising the temperature. I 

 myself have found that if the heart of the frog or toad be left till next 

 day, it is often apparently quite motionless, and then stimulation of 

 the conjoint vagus and augmentor nerves will make it beat again 

 strongly. I found, as might be expected, first, that this effect was due 

 to the augmentor fibres, and, secondly, that in reality the heart was not 

 still. A powerful lens showed in every case the existence of exceedingly 

 minute but regular contractions of the sinus and great veins, so that 

 although the auricles and ventricle were absolutely motionless, the sinus 

 contracted regularly. The standstill, in fact, was due to a block between 

 sinus and auricles, just as in the ordinary case of a dying heart a block 

 is first caused between auricles and ventricle, and then between auricles 

 and sinus. The case, then, was not a case of motor action upon a quiescent 

 heart, but a very striking example of the power of the augmentor nerve 

 in removing a block to the passage of the contraction wave. Similarly, 

 with regard to Schelske's experiment, the blocking power of heat upon 

 the passage of the contraction from auricle to ventricle, and the removal 

 of that block by stimulation of the augmentor fibres of the vagus nerve, is 

 shown in my Philosophical Transactions paper, Fig. 17, PL LXIX. On the 

 other hand, Lowit 3 showed, in 1882, that when the heart of the frog had 

 been brought to standstill by the application of muscarine, stimulation of 

 the vagus nerve was able to cause such a quiescent heart to beat strongly. 

 I myself 4 have repeated his experiment, and found that here too it is the 

 augmentor nerve which causes this effect, and apparently without any 

 sign of beating in the sinus. I found, however, that a further dose of 



l Journ. Physiol., Cambridge and London, 1892, vol. xiii. p. 407. 



2 ' 'Ueber die Veranderungender Erregbarkeit durch die AVarme," Heidelberg, 1860, S. 20. 

 8 Arch. f. d. cjes. Physiol., Bonn, 1882, Bd. xxviii. S. 333. 



4 "On the Action of Muscarine upon the Heart, etc.,' - Journ. Physiol., Cambridge and 

 London, 1887, vol. viii. p. 404. 



