EFFECT OF CUTTING OFF THE BLOOD FROM THE BRAIN. 543 



The two experiments just' detailed show that ligature of the aorta has 

 no sensible effect upon respiration ; but that ligature of all the vessels given 

 off from the arch of the aorta, which, it would seem, must cut off the supply 

 of oxygenated blood from the brain and the medulla oblongata, produces a 

 sense of want of air, which gives rise to respiratory efforts, even while arti- 

 ficial respiration is efficiently maintained. It seems, from the results ob- 

 served in Experiment I., that it is not enough to tie the innominate artery, 

 which is equivalent to tying the two common carotids and the right sub- 

 clavian artery, but that it is also necessary to tie the left subclavian artery. 

 This is explained by the fact that the left subclavian gives off' the vertebral 

 artery, which empties into the basilar artery, and thus carries oxygenated 

 blood to the medulla oblongata. 



Taking into account the fact that the sole respirator}' nervous centre is 

 situated in the medulla oblongata, the two experiments which I have de- 

 scribed, as far as they go, seem to show conclusively that the sense of want 

 of air is due to a deficiency of oxygenated blood in the medulla oblongata, 

 and that this sense is satisfied by the circulation of such blood in the respira- 

 tory nervous centre. 



Experiment III., October 7, 1877. — A full-grown young dog, weighing 

 about thirty pounds, was brought completely under the influence of ether 

 at 10.45 A. M., a bellows was fixed in the trachea, and the chest and abdo- 

 men were opened as in the preceding experiments. The vessels given oft' 

 from the arch of the aorta were then carefull}^ dissected out, and loose liga- 

 tures were thrown around the innominate arterj^, the two carotids, the right 

 subclavian artery, the right vertebral artery, the left subclavian artery, and 

 the left vertebral artery. These ligatures were placed around the vessels 

 so that they might be readily found in the course of the experiment, but the 

 vessels were not thereby constricted. 



After these preparatory steps had been completed, artificial respiration 

 was arrested, and the animal began to make respiratory efforts in thirty 

 seconds. Artificial respiration was then resumed, and the animal became 

 quiet. 



The two subclavian arteries were then constricted with serre-Jines, which, 

 it was ascertained, arrested the blood-current completely. The animal re- 

 mained quiet for five minutes, making no respiratory efforts. The sub- 

 clavians remaining constricted, both carotids were then constricted in addi- 

 tion. The animal made respiratory efforts in two minutes and seven 

 seconds after constriction of the carotids. All the vessels Avere then freed, 

 and the animal became quiet. 



Both vertebral arteries and both carotids were then constricted for five 

 minutes, the animal remaining quiet. These vessels remaining constricted, 

 both subclavian arteries were constricted in addition. The animal made 

 respiratory efforts in one minute and thirty-five seconds. All the vessels 

 were then freed, and the animal became quiet. 



At 11.40 o'clock, the descending aorta in the chest, and both subclavian 



