482 RESPIRATION. 



Reid thought it was due in a measure to the circulation of 

 venous blood in the medulla oblongata. 1 What has been 

 shown to be the correct explanation was given by Yolkmann 

 in 1841. He regarded the sense of want of air as dependent 

 on a deficiency of oxygen in the tissues, producing an im- 

 pression which is conveyed to the medulla oblongata by the 

 nerves of general sensibility. By a series of experiments, this 

 observer disproved the view that this sense resides in the lungs 

 and is transmitted along the pneumogastric nerves ; and by 

 exclusion, he located it in the general system, and showed that 

 such a supposition is competent to explain all the phenomena 

 connected with the respiratory movements. 3 In the hope of 

 settling some of these questions, which might be regarded as 

 somewhat uncertain, we instituted, a few years ago, a series of 

 experiments, which were embodied in the paper already re- 

 ferred to. 3 In these observations, the following facts, some of 

 which had been previously noted, were demonstrated ; and 

 their results leave no doubt as to the location and cause of 

 the respiratory sense : 



1. If the chest be opened in. a living animal, and artificial 

 respiration be carefully performed, inflating the lungs suffi- 

 ciently but cautiously, and taking care to change the air in 



1 An Experimental Investigation into the functions of the Eighth Pair of 

 Nerves, etc. Part second. Anatomical and Physiological Researches, Edin- 

 burgh, 1848, p. 285 ; and Edinburgh Medical and Surgical Journal, 

 April, 1839. 



2 VOLKMANN, in Schmidt's Jahrbucher, 1842, p. 290. Volkmann shows that 

 after division of the pneumogastrics, an animal dies when deprived of air, not 

 calmly, but with undoubted symptoms of distress from suffocation, as if it had 

 been strangled without previous division of the vagi. He also made a number of 

 experiments, in which respiratory efforts continued for many minutes after extir- 

 pation of the lungs, in cats and dogs, care being taken to leave the phrenic nerves 

 intact. He goes on to reason that the sense of want of air must reside in the gen- 

 eral system, that it is due to a deficiency of oxygen, and that its exaggeration 

 constitutes the sense of suffocation. His observations do not show, however, 

 that this is not due to the presence of carbonic acid, as has been supposed by 

 many. Vierordt is of the opinion that the respiratory sense is due to the circu- 

 lation of the venous blood in the substance of the nerves. 



3 American Journal, October, 1861. 



