83 



foetus of the mammalia, are inert, and not called 

 into use until the animal exchanges his watery habi- 

 tation for an aerial one, when the gills gradually 

 shrink *. Hence, then, it appears, that however 

 various the structure of the lungs in this class of ani- 

 mals may be, a more or less constant supply of fresh 

 air is required to enable them to support the func- 

 tions of animal life. 



68. To obtain a knowledge of the specific changes 

 which the air suffers by the respiration of the am- 

 phibia, the following experiments were instituted. 

 A toad, supported on a small hoop, was inclosed in 

 one hundred and eight cubic inches of atmospheric 

 air contained in a jar inverted over water, and stand- 

 ing in a room varying from 55 to 60 Fahren- 

 heit. He died on the fifth day. The water had ri- 

 sen considerably into the jar, and the residual air 

 was still farther diminished by agitation with lime- 

 water, which it rendered turbid. Fifty parts, after 

 being washed in lime-water, were next shaken in 

 the eudiometer with the liquid sulphuret of potassa, 

 and lost only one part of its bulk. The experiment 

 was repeated by confining another toad, in the same 

 manner, in another jar containing forty cubic inches 

 of atmospheric air, inverted over mercury. Un- 

 der the hoop which supported the animal, was 

 placed a small cup containing 1.5 cubic inch of the 

 water of potassa, which floated on the mercury. The 

 whole was then set aside in a room, of the tempe- 

 rature of 64. By the twelfth hour, the mercury had 



* John Bell's Anatomy, vol. ii. p. 1S2. 

 F 2 



