466 Dr. J. A. Mac William. Influence of the Central [May 18, 



It need hardly be remarked that if strong chloroform, vapour be 

 too suddenly administered, well-marked reflex slowing of the heart 

 may occur, as is well known ; and such slowing may precede what I 

 have described as the first stage or stage of acceleration. 



Evidence as to the mode in which chloroform brings about the 

 alterations in the cardiac rhythm which have been mentioned is 

 afforded by the results of the subsequent series of experiments. 



2. Experiments after Section of the Cardiac Augmentor Nerves, the 

 Vagi being left Uninjured. 



Those nerves were divided by an operation in which resection. of 

 the two uppermost ribs was performed, artificial respiration being 

 maintained ; the inferior cervical and the 1st thoracic (stellate) 

 ganglia, together with the annulus of Yieussens, were completely re- 

 moved on both sides, their connexions with the spinal nerves and the 

 vagi being followed up for a considerable distance and divided. The 

 sympathetic chain was cut through about 2 cm. above the inferior 

 cervical ganglion, and about the same distance below the ganglion 

 stellatum. The vagi themselves were left intact. 



No blood vessels were tied, and there was nothing beyond a very 

 inconsiderable loss of blood in the whole proceeding. 



When the influence of the cardiac augmentor nerves has been ex- 

 cluded in this way there is no essential change evident in the action 

 of chloroform upon the cardiac rhythm ; the stage of acceleration (A) 

 and that of moderate or slow rate (B) are still plainly apparent 

 during the lighter and the more profound phases of anaesthesia. It 

 is clear, then, the augmentor nerves are not the essential channels 

 through which chloroform produced its important effects upon the 

 pulse rate. 



3. Experiments in which the Vagi were Divided, the Cardiac Augmentor 



Nerves remaining Intact. 



The results obtained in this set of experiments were so essentially 

 similar to those of the following group that the two may be taken 

 together. The presence of the intact augmentor nerves does not seem 

 to be of any essential importance as far as the effect of chloroform on 

 the cardiac rhythm is concerned. 



4. Experiments in which all the Cardiac Nerves were Divided, all Direct 



Connexion between the Heart and the Central Nervous System being 

 thus Severed. 



In this condition the heart beats very rapidly, being liberated from 

 the controlling influence of the cardio-inhibitory centre in the medulla. 



