RESPIRATION. 625 



no method of proving that the effects of these gaseous bodies up- 

 on the coagulated blood are the same as they would be on the 

 blood in its natural state, circulating in the vessels of a living 

 animal. The facts which have been ascertained are the follow- 

 ing : 



1st. It appears from the experiments of Priestley, Girtanner, 

 and Hassenfratz, that when venous blood is exposed to oxygen 

 gas confined over it, the blood instantly assumes a scarlet colour. 

 Davy could not perceive any sensible diminution of the bulk of 

 the gas. 



2d. The same change of colour takes place when blood is ex- 

 posed to common air. In this case a quantity of carbonic acid 

 gas is formed, and a quantity of oxygen gas, exactly equal to it 

 in bulk, disappears ; making allowance for the small quantity of 

 carbonic acid, which we may suppose to be absorbed by the blood 

 itself. 



3d. Venous blood exposed to the action of azotic gas conti- 

 nues unaltered in colour ; neither does any perceptible diminu- 

 tion of the gas ensue. 



4th. Venous blood exposed to the action of nitrous gas be- 

 comes of a deep purple, and about one-eighth of the gas is ab- 

 sorbed. 



5th. Venous blood exposed to nitrous oxide becomes of a 

 brighter purple, especially on the surface, and a considerable 

 portion of the gas is absorbed. 



6th. Venous blood exposed to carbonic acid gas becomes of a 

 brownish-red colour, much darker than usual, and the gas is 

 slightly diminished in bulk. 



7th. Carburetted hydrogen gas gives venous blood a fine red 

 colour, a shade darker than oxygen gas does, as was first observ- 

 ed by Dr Beddoes, and at the same time a small portion of the 

 gas is absorbed. This gas has the property of preventing, or at 

 least greatly retarding the putrefaction of blood, as was first ob- 

 served .by Mr Watt* 



8th. When arterial blood is put in contact with azotic gas, or 

 carbonic acid gas, it gradually assumes the dark colour of venous 

 blood, as Dr Priestley found.f The same philosopher also ob- 

 served, that arterial blood acquired the colour of venous blood 

 when placed in vacuo.\ Consequently this alteration of colour 



* Davy's Researches, p. 380. f Priestley, iii. 363. 



\ Priestley, iii. 363, and Ann. de Chim. ix. 269. 



R r 



