180 



experiment by which the carbon could be supplied, 

 we must refer its production to that source. The 

 formation of this acid was found also by Spallanzani 

 to depend very much on temperature ; for snails con- 

 sumed more oxygen, and died in equal bulks of air, 

 much sooner when the temperature was mild, than 

 when it was severe * \ and, by gradually reducing 

 the temperature, he at length reached that point 

 where the air in which the snails were confined, un- 

 derwent no change at all ; which point he found to 

 be at zero t The circulation all this time was gra- 

 dually declining, and at 1 Reaum. the pulsations 

 altogether ceased, the heart remained perfectly at 

 rest,and the whitish fluid usually flowing in the vessels 

 was in a state of stagnation {. Nearly similar results 

 were obtained from another species of snails in a 

 hybernating state. In these, the covering or opercle 

 with which they close up their shell in winter, effec- 

 tually excludes the air on that side, neither does it 

 penetrate their shells elsewhere ; for a small glass 

 tube, filled with mercury, being inserted into this 

 covering, and then inverted, sustained a column of 

 28 inches of that fluid, which corresponded to the 

 height of the mercury in an adjacent barometer. 

 When, however, the covering was punctured so as 

 to admit the air, it instantly forced down the mer- 

 cury. The small portion of air contained in these 

 shells for several months during the torpid state of 

 the animals, was found in several trials to be of like 



* Memoirs on Respiration, p. 150. 

 | Ibid. p. 152. \ Ibid, p. 151. 



