The next inquiry regarded _stagnant water renewed at intervals_, and in this the duration of life was prolonged beyond the term of the last experiments, and even to eight days. During winter when the temperature was lowest the frogs remained active, though less so than in spring.
The conclusions to be drawn from these experiments are, that frogs pass the winter _in an animated state in water_, not becoming stiffened as in ice, and that they need not to approach the surface of the water in order to respire, provided the water they inhabit be _renewed at intervals_; but if the water be not renewed, or if disaërated water be employed, the frogs perish.
Considering that these animals are truly amphibious, these results are very curious; and it is interesting in a physiological point of view, to know that frogs are able to respire the air contained in the dense medium of water for an indefinite period, and just as easily as they breathe the finer medium on land.
Respecting the action of aërated water on the skin, the conclusion drawn seems to be correct, that it must be from _cutaneous_ absorption that the air contained in the water promoted the continuance of life in Dr. Edward’s experiments upon this point, since the animals were in a state of _asphyxy_ regarding respiration by the lungs; and that no [p149] air entered in combination with water was shewn from Dr. Edwards _never having seen water in the lungs_. Therefore, unless the air acted on the blood through some other organ, the lives of these animals would be definite and shortened, even though the water be renewed from time to time, and their _asphyxy_ would be complete and continued. And since the skin is the only organ in contact with the air, it is fair to conclude that it is the medium of aërial absorption.
When the _webs_ were examined under water, these membranes indicated the action of air upon their blood-vessels, by the bright tint of the blood.
Spallanzani imagined that frogs perish sooner in _running_ than in _stagnant_ water; but Dr. Edwards having secured some of these animals in ten feet of the Seine, whilst others were simultaneously placed in _unrenewed stagnant water_, he found the latter did not survive many hours, and the former lived a long time.