it ogen ; so that much less nitrogen gas was de- 

 stroyed in this case by two snails, than in the 

 former experiments by one. In other experiments 

 with snails, he has more than once found the whole 

 eighty parts of nitrogen gas remaining ; and the 

 helix vivifiara consumes all the oxygen gas of the 

 air without producing any increase or diminution of 

 the nitrogenous portion *. These facts, taken in 

 connection with the apparently decisive experiments 

 of Vauquelin, and those of the author himself with 

 regard to slugs, lead us to the direct conclusion, that 

 in the respiration of slugs, worms^ and snails, the 

 whole of the oxygenous portion of the atmosphere 

 completely disappears ; that carbonic acid is, in all 

 cases, produced, and that the nitrogen gas remains 

 unaltered. 



6 1 . Nearly the same results were obtained by ex- 

 periments on the respiration of another species of 

 snails, whose residence is wholly in the water. Spal- 

 lanzani found, that the helix vivifiara, which inhabits 

 still rivers and pools, consumed, by its respiration, 

 the oxygen gas of the atmosphere, like snails which 

 live on the land : that this action did not go on in 

 temperatures a few degrees only above the freezing 

 point, but was very considerable in higher tempera- 

 tures : that water, deprived of its air by boiling, did 

 not support life, neither did it, when freed from its 

 oxygen gas, and standing in contact with nitrogen 

 gas : that snails, confined to the bottom of a jar of 

 water, consumed only half the quantity of air that 

 those did which were allowed to come to the surface : 



* Memoirs on Respiration, p. 21 4s 301. 



