166 KESPIRATIOK 



expose an artery and note the color of the blood as it flows, it will be observed that the 

 respiratory efforts commence only when the blood in the vessel begins to be dark. When 

 artificial respiration is resumed, the respiratory efforts cease only when the blood becomes 

 red in the arteries. 



3. If, while artificial respiration is being regularly performed, a large artery be opened 

 and the system be thus drained of blood, when the haemorrhage has proceeded to a cer- 

 tain extent, the animal makes respiratory efforts, which become more and more violent, 

 until they terminate, just before death, in general convulsions. 



These facts, which may be successively observed in a single experiment, remain pre- 

 cisely the same if we previously divide both pneumogastric nerves in the neck ; showing 

 that these are by no means the only nerves which convey the respiratory sense to the 

 medulla oblongata. 



The conclusion which may legitimately be drawn from the above-mentioned facts is 

 that the respiratory sense does not originate in the lungs, for it operates when the lungs 

 are regularly filled with pure air, if the system be drained of the oxygen-carrying fluid. 



In 1877, we repeated and extended the experiments just mentioned (New York Medical 

 Journal, November, 1877). The new experiments were made upon dogs, in the follow- 

 ing way : The animals were brought under the influence of ether, the chest was opened, 

 and artificial respiration was carried on by means of a bellows fixed in the trachea. The 

 great vessels given off from the arch of the aorta were isolated so that they could be sep- 

 arately constricted at will. In a number of experiments upon different animals, the in- 

 nominate artery and the left subclavian were constricted, and the animal began to make 

 respiratory efforts in from two minutes and five seconds to two minutes and eight sec- 

 onds after, although artificial respiration was kept up constantly and efficiently. The 

 animals made no respiratory efforts when the vessels given off from the arch of the aorta 

 were left free and when the aorta was tied in the chest, which cut off the supply of blood 

 from the trunk and the lower extremities. In the experiments in which the vessels 

 going to the head and upper extremities were constricted, the respiratory efforts always 

 ceased when the vessels were freed. 1 



In our experiments upon the location of the sense of want of air, made in 1861, we 

 thought that they proved experimentally that the sense of want of air is due to a 

 deficiency in oxygen in the system at large. The main features of the experiments made 

 at that time have been already stated. Our object in making these new experiments was 

 to study the effects of cutting off the supply of oxygenated blood from different parts. 

 It may be assumed that the sole respiratory nervous centre is in the medulla oblongata, 

 and we endeavored to devise some means of cutting off the arterial supply of blood from 

 this part. Animals respire when all of the encephalic centres have been destroyed ex- 

 cept the medulla oblongata, so that it is improbable that cutting off the supply 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 must be deprived 

 of oxygenated blood. 



In one experiment (1877), the innominate artery and the left subclavian artery were 

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

 notwithstanding that artificial respiration was kept up. 



In another experiment, the same vessels were constricted, and the animal made respir- 

 atory efforts in two minutes and five seconds. 



In a third experiment, both subclavian arteries and both carotids were constricted, 



1 The reader is referred to our original article for a complete account of the details of these experiments. In Her- 

 mann, Grurtdiss der Physiologic, Berlin, 1870, S. 160, and in Foster, Text-Book of Physiology, London, 1877, p. 

 254, the respiratory efforts are attributed to " an accumulation of carbonic acid and a paucity of available oxygen " in 

 the medulla oblongata, but this view lacked the positive experimental proof afforded by our experiments of 1S77. 



