. VI. EFFECTS OF RESPIRATION. 123 



in the lungs during the act of respiration. Bichat divided 

 both the trachea and arteries of a dog, and immediately 

 applied a stop cock to the opening of each of these vessels. 

 By closing the stop cock of the trachea, shortly after an in- 

 spiration, the arterial blood became blackish, and before it 

 had flowed a minute was completely venous. On repeat- 

 ing the experiment, and closing the stop cock as soon as 

 possible after an expiration, the arterial blood flowed for a 

 few seconds, and was of a black colour. When we re- 

 moved the air from the lungs, by means of an air-pump, 

 the blood immediately issued from the artery, black ; when, 

 on the contrary, we threw a little air into the lungs, the 

 blood preserved for a longer time its vermilion colour. By 

 carefully opening, from time to time, the stop cock of the 

 trachea, an alternate shower of red and black blood was 

 obtained. 



Here is a rabbit, to the trachea of which a stop cock is 

 fixed : observe the peritoneum which has been exposed. 

 You perceive that the red colour of these vessels changes 

 to a deep red when the stop cock is kept closed for a few 

 moments, but returns to its natural tint when the stop cock 

 is re-opened. In asphyxiated animals the tissues of all parts 

 of the body, the kidneys, the muscles, the tongue, and the 

 lips, assume a blackish colour. If the two pneumo-gastric 

 nerves of an animal be divided, the respiratory movements 

 soon become disturbed; and at the same time all the blood 

 preserves its black colour, and the lips, the nostrils, and the 

 pharynx of the animal lose their red tint. 



If, instead of introducing atmospheric air into the lungs 

 of an animal, we make it breathe azote, carburetted hydro- 

 gen, pure hydrogen, carbonic oxide, carbonic acid, binoxide 

 of azote, or sulphuretted hydrogen, death takes place more 

 or less rapidly, and the blood of every part of the body is 

 found black. Besides atmospheric air, oxygen and protox- 



