474 Dr. J. A. MacWilliam. Influence of the Central [May 18, 



is done, an afferent nerve (which was found to give marked reflex 

 acceleration as long as the vagi were intact) can now be stimulated 

 as before, with the result of causing evident manifestations of general 

 motor excitement, shown by the occurrence of marked convulsive 

 movements ; but in this case there is no cardiac acceleration. The 

 moderate rhythm maintained by slight continued excitation of the 

 vagus is not appreciably interfered with by stimulation of afferent 

 nerves ; and this negative result I have obtained in every experiment 

 with complete constancy. It strongly opposes the idea that the 

 sudden and extensive acceleration frequently seen on stimulating 

 afferent nerves is due to a reflex action of the augmentor nerves ; for, 

 as soon as the vagi are cut, no reflex acceleration occurs, even when, 

 as in these experiments, the heart was kept beating at a moderate 

 rate, a condition favourable to the marked manifestation of the in- 

 fluence of augmentor excitation upon the cardiac rhythm.. 



3. The results of excitation of afferent nerves, after section of the 

 cardiac augmentor nerves, the integrity of the vagi not being interfered 

 with. — The augmentor nerves were cut by a mode of operative pro- 

 cedure already stated. That the vagi remained uninjured was shown 

 by their being readily excited through a rise of blood pressure or by 

 a suitable stimulation of certain afferent nerves, well marked slowing 

 of the heart being evident in each case. 



In this condition, the cardiac augmentors being now excluded, 

 stimulation of afferent nerves, which caused acceleration prior to 

 section of the augmentors, can still cause a very marked quickening 

 of the pulse rate. In the case of the brachial or intercostal nerves, 

 for example, stimulation (mechanical or electrical) leads, in favour- 

 able circumstances, to a very decided change in rhythm, provided as 

 before that the stimulation is also effective in causing general motor 

 excitation ; an acceleration is speedily induced, frequently to the 

 extent of 20 per cent., but sometimes much more. 



In some cases a brief phase of cardiac slowing is also seen; and 

 in other instances a more or less regular alternation of phases of 

 slowing and acceleration presents itself. The same general relation 

 already noted as obtaining between the strength and suddenness of 

 the stimulation, the excitability of the medullary centres (depending 

 on depth of anaesthesia), and the nature of the change in rhythm as 

 regards the occurrence of slowing or acceleration, is again observable 

 here ; also the notable difference between the splanchnic and somatic 

 nerves, as regards the constant association of general motor excite- 

 ment with the reflex cardiac acceleration which occurs in the latter 

 case, and the frequent absence of any such association in the former. 



In short, the action of afferent excitation upon the cardiac 

 rhythm, as far at least as its main features are concerned, is essenti- 

 ally similar whether the augmentor nerves are divided or intact. 



