EFFECT OF CUTTING OFF THE BLOOD FROM THE BRAIN. 545 



the medulla oblongata, so that it is improbable that cutting off the supplj 

 of blood from the brain would affect the muscles of respiration, provided 

 that artificial respiration be efficiently maintained. Blood can get to the 

 medulla oblongata from the internal carotids, which are connected with the 

 circle of Willis, from the vertebral arteries, which unite to form the basilar 

 artery, -'^ and perhaps from other vessels; but it is certain that, if all the 

 arteries given off from the arch of the aorta be tied, the medulla oblongata 

 must be deprived of oxj^genated blood. 



In Experiment I. , the innominate artery and the left subclavian artery 

 were constricted, f and the animal made respiratory yftbrts in two minutes 

 and eight seconds, notwithstanding that artificial respiration was kept up. 



In Experiment II., the same vest^els were constricted, and the animal 

 made respiratoiy efforts in two minutes and five seconds. 



In Experiment III., both subclavian arteries and both carotids were 

 constricted, and the animal made respiratory efforts in two minutes and 

 seven seconds. Both vertebral arteries and both carotids were constricted, 

 and the animal made no respiratory efforts for five minutes ; but respira- 

 tory efforts were made in one minute and thirty-five seconds after both sub- 

 clavians had been constricted in addition to the vertebrals and carotids. 



It seems, from all of these experiments, that, in order to induce respira- 

 tory eftbrts in an animal under the influence of ether and with the lungs 

 supplied with air by artificial respiration., either the innominate artery and 

 the left subclavian arter}^, or both subciavians, both carotids, and both ver- 

 bral arteries, must be tied. In other words, according to niy views of the 

 cause of these respiratoiy efforts, the supply of blood to the medulla ob- 

 longata cannot be cut off completely except by tying all the vessels given 

 off from the arch of the aorta. 



As the result of the experiments which I have just detailed, I must now 

 modify the view which I advanced in 1861 as a conclusion from experiments 

 then published, M^iich I have maintained up to the present time, that the 

 sense of want of air, which is the starting-point of the movements of respira- 

 tion, is due to want of oxygen in the general system. My experiments 

 made in 1861 were accurate, and the conclusions from them seemed to be 

 legitimate; but these experiments were incomplete. The experiments 

 which I have just reported, taken in connecti-^n with my experiments of 

 1861, lead me to conclude that the sense of want of air is due to a want of 

 circulation of oxygenated blood in the medulla oblongata. 



I trust that my experiments, which are by no means difficult, or uncer- 

 tain in their results, may be repeated and verified or corrected, by other 

 physiologists. The idea that the sense of want of air is due to a deficiency 

 of oxygen in the medulla has been adopted by some writers ; but, as far as 



*The basilar artery is much longer in tbe dog than in the human subject. 



tin the first experiment, the great veins were also tied, but this seemed to make no 

 difference in the phenomena following constriction of the arteries, and the veins were left 

 free in the other experiments. 



