LECT. VI. AIR RESPIRED. 121 



which also exists there. The proportion of oxygen con- 

 tained in a definite volume of air dissolved in water, exceeds 

 that met with in atmospheric air. Humboldt and Gay 

 Lussac found in air obtained from fresh water 32 per cent- 

 of oxygen. According to Morren, the quantity of oxygen 

 in sea water appears to vary at different hours of the day, 

 and is at a maximum about noon ; the reverse holds good 

 for the carbonic acid. 



Fishes absorb a portion of this dissolved oxygen, and 

 yield up carbonic acid, which is absorbed by the water ; and 

 it is only by the continued solution of fresh portions of at- 

 mospheric air that the respiration of these animals can go on. 

 This is the reason why they quickly die in water deprived 

 of air by ebullition, or in water covered with oil. 



I may here mention an experiment which I made some 

 time ago on the respiration of the torpedo. The air dis- 

 solved in the water of the Adriatic, taken near the shore, 

 consists, in 100 parts, of 11 carbonic acid, of 60-5 azote, 

 and 29-5 oxygen. A large torpedo was kept for 45 minutes 

 in about a gallon of this water. The animal was frequently 

 excited, gave many shocks, and soon died. The air dis- 

 solved in the water, did not yield a trace of oxygen, but 

 contained 36 per cent, of carbonic acid, the remaining parts 

 in the hundred being azote. 



Experience has proved, that these changes in atmospheric 

 air, effected by contact with a living animal, take place not 

 only in the lungs, but also, in different degrees, at the entire 

 surface of the body of the animal. Frogs, confined in a 

 definite quantity of air, and either deprived of their lungs 

 or in some way prevented from carrying on pulmonary respi- 

 ration, continue to live. After some time, it is found that 

 a portion of the oxygen has disappeared, and has been re- 

 placed by carbonic acid. 



Humboldt and Provencal observed, that tench live with- 



