544 EFFECT OF CUTTING OFF THE BLOOD FROM THE BRAIN, 



arteries were tied. This left little more than the carotids to carry blood to 

 the head, and the arterial blood was thus cut off from the greatest part of 

 the system. The animal remained quiet for five minutes. The experiment 

 had now lasted fifty-five minutes, and the action of the heart had become 

 considerably ■ weakened. While the aorta and subclavians were still con- 

 stricted, both carotids -were constricted in addition. The animal remained 

 quiet for five minutes, but the heart and great vessels up to the points of 

 constriction were enormously distended. At the end of this time, the aorta 

 was freed, which relieved the distension. The animal made respirator}' 

 efforts in two minutes and twenty-nine seconds, but the efforts were liot 

 very violent and were not as rapid as usual. All the vessels were freed 

 and the animal became quiet. 



Artificial respiration was then arrested, and the animal made respira- 

 tory efforts in twelve seconds. Artificial respiration was resumed, and the 

 animal became quiet. 



The innominate artery and the left subclavian artery were then con- 

 stricted, and the animal made respiratory efforts in one minute and fifteen 

 seconds, but the action of the heart had become very feeble. 



The experiment had lasted one hour and fifteen minutes, and was con- 

 cluded with the last observation. 



In this experiment, I was assisted by Dr. C. F. Eoberts, Mr. Gaspar Gris- 

 wold, and Dr. G. S. Conant. 



This experiment substantially confirmed the results obtained in Experi- 

 ments I. and II, When the aorta, both subclavian arteries, and both caro- 

 tids, were constricted, the pressure of blood in these vessels was enormous, 

 and some blood may have found its way to the brain and medulla oblongata. 

 The distension of the vessels was so great that this part of the experiment 

 was not very satisfactory. Eespiratory efforts were made by the animal, 

 however, when the distension was relieved by freeing the aorta, the sub- 

 clavians and the carotids remaining constricted. 



In all the experiments, the animals were kept completely under the in- 

 fluence of ether, and artificial respiration was kept up efiiciently unless 

 otherwise stated. 



Deductions and Conclusions. — When I made my first experiments upon 

 the location of the sense of want of air which gives rise to respiratory move- 

 ments, in 1861, I attached to them considerable importance, and I thought 

 that I had proved experimentally that the sense of want of air is due to a 

 deficiency of oxygen in the system at large. The main features of the ex- 

 periments which I made at that time I have already stated. My object in 

 making these new experiments was to fetudy the effects of cutting off the 

 supply of oxygenated blood from different parts. 



I think it can be assumed, as I have already stated, that the sole respira- 

 tory nervous centre is in the medulla oblongata, and I endeavored to devise 

 some means of cutting off the arterial supply of blood from this part. Ani- 

 mals respire when all of the encephalic centres have been destroyed except 



