76 



that the water attracts oxygen gas to supply the place 

 of that which is consumed ; and that, when confined 

 in air only, these snails, by means of their skins, 

 consume all the oxygen gas, and produce carbonic 

 acid, without changing the quantity of nitrogen gas*, 

 62. Other aquatic animals, as muscles (niytilus e- 

 didis} were next confined in a jar, and water was 

 poured over them to the depth of an inch. They 

 soon opened the thinnest part of their shell, and, in 

 ten or fifteen minutes more, threw out a small quan- 

 tity of water : the shells were then shut again for a 

 few minutes, and this action was alternately repeat- 

 ed. When two of these muscles were placed in a 

 tube, half filled with water and half with air, in a 

 temperature of about 66 Fahrenheit, they continued 

 to live seven days, and, on the eighth day, the oxy- 

 gen gas of the air was considerably diminished. 

 With a portion of oxygen gas occupying the supe- 

 rior part of the vessels, these muscles would live nine 

 days, but when nitrogen gas was in the same way 

 employed, they died in three days. In every case, 

 whatever quantity of nitrogen gas was present, it al- 

 ways remained unchanged f. On several species of 

 marine testacca, he likewise made experiments, and 

 found that they consumed the oxygen gas of sea- 

 water, which attracts more to supply the waste ; that 

 when confined in air only, they consume all its oxy- 

 gen gas, and that they soon perish when nitrogen 

 gas only is made to rest on the water, producing no 

 change upon it J. 



* Memoirs on Respiration, p 288. 296. 301. 



f Ibkl. p. 304. 306. 309. J Ibid, p, 311. et scq, 



