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



IV. " On the Influence exercised by the Central Nervous System 

 on the Cardiac Rhythm, with an Inquiry into the Action of 

 Chloroform on that Rhythm."* By John A. MacWilliam, 

 M.D., Professor of the Institutes of Medicine in the Uni- 

 versity of Aberdeen. Communicated by Professor M. 

 Foster, Sec. R.S. Received March 23, 1893. 



The following is a brief accountf of the main results obtained in 

 the course of a prolonged investigation of the above subject. 



The animals employed were chiefly cats and rabbits, anaesthetised 

 or narcotised with chloroform or chloral hydrate. In the great 

 majority of the experiments, cats were used anaesthetised with chloro- 

 form ; and it is the results obtained in those circumstances that I am 

 to be understood as specially dealing with in this paper. 



The chief object of the present investigation was to examine more 

 fully the mechanism through which changes in the pulse rate are 

 effected and the nature of those changes, when such are dependent on 

 an influence exercised by the central nervous system upon the cardiac 

 rhythm, e.g., the changes in the pulse rate induced by afferent im- 

 pulses, &c. 



In proceeding to examine the influence of the nervous system on 

 the cardiac rhythm, it is necessary in the first place to determine the 

 conditions depending on the presence of the anaesthetic, as far as they 

 bear on the cardiac rhythm, the influence of chloroform upon the 

 heart itself and upon the centres of the cardiac regulating nerves. 



I. On the Relation of Chloroform to the Cardiac Rhythm. 



With a view to the elucidation of this question, I have carried out 

 the following series of experiments, to test the action of chloroform 

 under different conditions and so determine the manner in which it 

 may affect the rhythmic mechanism of the heart : — 



1. Experiments in which the entire cardiac regulating mechanism 

 was intact/ 



2. Experiments after section of the cardiac augmentor nerves, the 

 vagi being left uninjured. 



3. Experiments in which the vagi were divided, the cardiac 

 augmentor nerves remaining intact. 



4. Experiments in which the whole of the cardiac nerves were 

 divided, all direct connexion between the heart and the central 

 nervous system being thus severed. 



* The expenses of this research were for the most part defrayed by a grant from 

 the Royal Society. 



f Full details and references are stated in a longer paper, soon to be published. 



