544 Roijal Society : — 



temperature, I find tliat, at each effort it makes to inspire, the 

 heart either ahiiost suddenly stops, or beats much less quickly. 



I have frequently seen the heart completely arrested for five or 

 ten seconds, and twice for twenty or twenty-tive seconds, in cases 

 where there was only one respiration in two minutes. This stoppage 

 of the heart's movements was the more remarkable, as they were at 

 the rate of more than two hundred in a minute when the effort at 

 inspiration took place. To decide that it was in consequence of an 

 influence of the par vagum that this occurred, I divided this nerve 

 in the neck, and th^n found that there was no more influence of the 

 inspiration on the heart, or if there was, it consisted in an augment- 

 ation of the frequency of the movements of this organ — an augment- 

 ation due to the shaking of the heart when the chest dilated 



Sometimes, when the heart was very irritable, and when the efforts 

 at inspiration were still frequent and not energetic (the par vagum 

 being undivided), these efforts were accompanied, or rather imme- 

 diately followed by an increase in the strength of the heart's move- 

 ments, probably caused by the shaking. But always when the 

 inspiratory efforts were energetic and rare, they coexisted with a 

 diminution or a momentary cessation of the heart's contractions ; 

 and always in these cases the section of the par vagum has destroyed 

 the diminishing influence of the respiratory efforts on the heart. 

 It would be esrsy to show that the influence of the inspiratory effort 

 on the central organ of circulation is comparable to the change 

 taking place in the pupil when the globe of the eye is drawn inwards : 

 it is an associated action. 



From the facts I have found in the case of newly-born animals and 

 birds, and from the facts observed in man by Professors J. Midler, 

 Bonders, and others, it results that, during efforts at inspiration, a 

 nervous influence passes along the par vagum from the medulla 

 oblongata to the heart, diminishing the movements of this organ. 

 And as by an action of our will we may inspire with energy, it 

 follows that we can by an influence of our will diminish the action 

 of our heart, just as we can contract our pupil by drawing our eyes 

 inwards. 



•' On the Influence of Oxygen on the vital properties of the Spinal 

 Cord, Nerves, and Muscles." By E. Brown-Sequard, M.D. 



The influence of oxygen and carbonic acid on the living tissues, 

 has been very little investigated, either by physiologists or practi- 

 tioners of medicine. I have made a great many experiments on 

 this subject, but will relate here merely a few of them, which are 

 sufficient to show that oxidation of the spinal cord and nerves, as 

 well as that of muscles, increases their vital properties, sometimes 

 in a high degree. 



After the opening of the sj)inal canal, the dura mater being laid 

 bare, we find that an evident hyperresthesia a])pears after a short 

 time in the parts of the body which are behind the opening, and 

 also on the same level with it, and a little above it. I think 

 this increase of sensibility depends on the absorption of oxygen. 

 To ascertain that it is so, with the help of a special apparatus, im- 



