EXPERIMENTS OF EDWARDS. 831 



In like manner, it is evidently owing to the 

 torpid state of the circulation in reptiles, fishes, 

 worms, and zoophytes, that they live so much 

 longer in vacuo and the mephitic gases, or when 

 greatly mutilated, than warm blooded animals ; 

 and that even the latter require but little air to 

 support a low degree of vitality, when reduced to 

 a state of torpor by external cold. Hence it is, 

 that frogs remain for weeks, and even months 

 under water, (which contains only about 3 per 

 cent, by volume of air, according to Humboldt,) 

 during winter, or so long as the mean tempera- 

 ture of the ponds and marshes in which they 

 reside is below 50. 



Dr. Edwards performed some experiments on 

 frogs and salamanders, which led him to suppose 

 that they are capable of living in aerated water 

 at temperatures below 50 by cutaneous respira- 

 tion; because when strangled by placing a liga- 

 ture around the throat, and placed in a receiver 

 containing atmospheric air, they remained alive 

 from one to two hours ; and when taken out of 

 the vessel, it was found to contain a sensible 

 quantity of carbonic acid. He further states, that 

 when the heart of salamanders was removed by 

 excision, they lived from twenty-four to twenty- 

 six hours in the atmosphere, but only from eight 

 to nine hours when immersed in cold water at the 

 same temperature: that when the lungs of frogs 

 were extirpated, they lived from one to five days 



