144 Dr. Edwards, De V Influence 



they never altogether recovered their perfect freedom. As 

 a comparative illustration, an equal number of frogs were 

 submersed in water, all of which died in about ten or eleven 

 hours, while those which were strangled lived from one to 

 five days. Salamanders continued active longest, and one 

 did not cease to exist till the eleventh day, although during 

 this time he was in a complete state of asphyxy from perfect 

 strangulation. 



Dumeril once found that a salamander lived a long time 

 after decapitation, even when the cicatrix of the wound was 

 healed so as to stop all access of air to the lungs. 



In comparing the effects of strangulation with those of 

 submersion or drowning, it is to be supposed either that these 

 animals exist a limited period without the necessity of 

 the nervous system being in contact with atmospheric air, or 

 that the air influences their blood through the integuments 

 of the body. Accordingly Dr. Edwards put this to the test 

 by making experiments upon cutaneous respiration. 



Spallanzani found that the exposure of cold-blooded ani- 

 mals to the air was attended with exudation of carbon, a 

 phenomenon similar to that of respiration. There appears, 

 however, to be some source of error in these experiments, for 

 Spallanzani removed the lungs, and this operation rendered 

 the animal liable to the absorption of air and loss of blood. 

 Dr. Edwards sought to effect the same purpose by a different 

 and more successful measure. He also confined frogs in vessels 

 of atmospheric air, and fastened bladders round the head and 

 neck, tight enough to stop the entrance of air to the lungs. 

 At the expiration of two hours the air was examined in the 

 bladder, and it was found to contain an excess of carbonic 

 acid. The same result was obtained from salamanders. It 

 appears, therefore, that while air is in contact with the skin, 

 carbon is given out ; but whether this be the eflect of exhala- 

 tion merely, or that oxygen is actually absorbed, and carbon 

 transpired, is a question which led to further inquiries. Dr. 

 Edwards, therefore, inclosed cold-blooded animals in solid sub^ 

 stances, in order to determine the influence of dark-coloured 

 blood, free of all external agency, in the production of che- 

 mical changes, and to observe its sensible eft'ect upon the 

 nervous system. 



In the year 1779 three toads were confined in a box herme- 

 tically sealed, and so deposited in the Academy of Sciences. 

 Eighteen months after, the box was opened, and one toad 

 was found dead. These animals have been found alive in 

 blocks of coal after an imprisonment of some years, and have 



