158 CHANGES OF AIR AND BLOOD IN RESPIRATION. 



care to change the air in the bellows every few moments. So long as this 

 was continued, the animal made no respiratory effort ; showing 'that for the 

 time the respiratory sense was abolished. This was little more than a 

 repetition of the classical experiment of Robert Hook, an account of which 

 was published in 1664. 



When the artificial respiration was interrupted, the respiratory muscles 

 were thrown into contraction, and the animal made regular, and at last vio- 

 lent efforts. An artery was then opened and the color of the blood was 

 noted. It was observed that the respiratory efforts began only when the blood 

 in the vessel became dark. When artificial respiration was resumed, the re- 

 spiratory efforts ceased only when the blood became red in the arteries. 



While artificial respiration was being regularly performed, a large artery 

 was opened and the system was drained of blood. When the haemorrhage 

 had proceeded to a certain extent, the animal made respiratory efforts, which 

 became more and more violent, until they terminated, just before death, in 

 general convulsions. 



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

 remained precisely the same when both pneumogastric nerves had been 

 divided in the neck. 



The conclusion which may legitimately be drawn from the above-men- 

 tioned facts is that the respiratory sense does not always and necessarily 

 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. 



A similar conclusion was arrived at by Rosenthal (1862) and by Pfliiger 

 (1868). Pfliiger produced asphyxia in dogs by causing them to respire pure 

 nitrogen. In his experiments, he analyzed the blood after thirty seconds 

 and after one minute of inhalation of nitrogen. He found a great diminu- 

 tion in oxygen with very slight increase in carbon dioxide at the end of 

 thirty seconds. After one minute the oxygen was reduced from 14-35 per 

 cent, in volume to 0-2 per cent., and the carbon dioxide from 36-9 to 29-9. 

 As a conclusion he stated that " no one, therefore, can be of the opinion that 

 dyspnoea and asphyxia in breathing indifferent gases are connected with the 

 accumulation of carbon dioxide." 



In 1877 the experiments made in 1861 were repeated and extended (Flint). 

 The later experiments were made upon dogs, in the following way : The ani- 

 mals 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 separately constricted at will. In a number of experiments 

 upon different animals, the innominate artery and the left subclavian were 

 constricted, and the animal began to make respiratory efforts about two min- 

 utes after, although artificial respiration was kept up constantly and effi- 

 ciently. 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 ex- 

 tremities. In the experiments in which the vessels going to the head and 



