97 



the earth. In the native American, the inhabitant 

 of Asia, and the southern European, the colour va- 

 ries from dark copper to pale tawny ; and in the ne- 

 gro it is quite black. The inhabitants of the north- 

 ern countries, on the other hand, are white : and, 

 not only are those parts of the body, which are most 

 covered, the whitest, but a sensible difference in co- 

 lour exists in the same person at different seasons of 

 the year. These variations in colour have been held 

 to depend very much on the agency of light. 



82. The necessity of atmospheric air to the con- 

 tinuance of living action in all the superior animals, 

 was long ago proved by the experiments of Mr 

 Boyle, soon after the discovery of the air-pump ; 

 and he observed farther, that the function of respi- 

 ration is quickly suspended, unless the lungs are 

 furnished with a regular supply of fresh air *. " A- 

 nimals, whose hearts have two ventricles and no 

 foramen ovale, says Mr Derham, as birds, dogs, cats, 

 and mice, die under the action of the air-pump in 

 less than half a minute, counting from the very first 

 exsuction, especially in a mall receiver t" In cor- 

 roboration of these facts, we may mention an expe- 

 riment, exhibited before the Royal Society, by the 

 celebrated Dr Hooke. He cut away the ribs, dia- 

 phragm, and pericardium of a dog, whereby the 

 lungs and heart were brought into view ; and then, 

 dividing the windpipe, he introduced into it the 

 nozzle of a pair of double bellows, and made, at the 



* Boyle's Works, vol. i. p. 99. 

 f Physico-Theology, p. 8. 



