212 RESPIRATION. 



The empty condition of the arteries after death has been 

 ascribed by Dr. Carson to the thoracic vacuum. He states that, 

 if an animal is destroyed by admitting air into each pleura, the 

 arteries are found as turgid as the veins 2 ; but the same results 

 have not been obtained by others a ; and J presume that the ob- 

 struction in the lungs from the want of chemical changes, gradually 

 lessening the supply to the arteries, and producing accumulation 

 in the veins, together with the superior contractile powers of the 

 arteries, are, jointly, quite sufficient to explain the circumstance. 

 The effect of the obstruction in the lungs, while the left ventricle 

 continued to propel blood, was strikingly shown by Bichat, who 

 produced enormous congestion of the lungs, liver, spleen, &c. 

 by strangling animals slowly, and found much less if respiration 

 was completely arrested at once, so that the left ventricle ceased 

 to propel blood very soon after the obstruction in the lungs took 

 place. 5 The greater the space into which the former blood can 

 flow from the arteries, the less blood will they contain. Hence, if 

 a ligature is passed round the cavae, some quantity of blood is 

 found in the arteries ; if around the pulmonary artery, less ; and, 

 when the lungs have been kept distended after death by artificial 

 inflation after opening the chest, so that all their vessels might 

 be unfolded, the arteries have been found quite empty, though 

 there was no thoracic vacuum c , and though the effect of the left 

 ventricle of the heart was destroyed by a ligature on the aorta. 



Therefore, if Dr. Carson's experiments on this point are accu- 

 rate, I should ascribe the turgidity of the arteries when the pleura? 

 were filled with air, and the lungs compressed, to the diminution ; 

 and when this was not done, the emptiness of the arteries, to the 

 largeness, of the pulmonary space into which the blood could pass. 



The influence of suction has been thought by Dr. Carson to- 

 assist in explaining absorption. d 



Dr. Carson ascribes the effects experienced in elevated situ- 

 ations to the rarity of the atmosphere, by which it cannot compress 

 the blood sufficiently to aid the return of this fluid towards the 

 heart. Saussure e says, that when he was on the summit of the 

 Alps he experienced extreme fatigue and loss of muscular power, 



Med. Clrir. Trans, vol. xi. 



Dr. Fennel, The Philadelphia Journal, Nov. 1822. 



Recherches Physiologiques, p. 225. sq. 



Mr. Robert Hunter, Edinmirgh Journal, Oct. 1824. 



1. c. p. 167. e Voyage dans les Alpes. 



