140 



working *. Dr Goodwyn repeated these experi- 

 ments, both with common air and with oxygen gas, 

 on dogs, and on lizards and toads, whose lungs con- 

 sist only of a transparent bladder ; and he observed 

 the same changes of colour, according as the lungs 

 were supplied with or deprived of fresh air f. This 

 suddenness of effect seems wholly inconsistent with 

 the supposed entrance of air into the blood, and its 

 subsequent decomposition during the circulation of 

 that fluid ; and favours the probability of its being 

 actually decomposed in the lungs. 



114. Not only, however, in the lungs, but in 

 the bronchial cells pf those organs does this de- 

 composition appear to happen, of which the vast ex- 

 tent of their surface is a strong presumptive proof. 

 Dr Hales estimates the capacity of each cell, in the 

 lungs of a calf, at the ~ part of an inch diameter, 

 and the surface of all the cells together at 4O,000 

 square inches, to which, if 1635 square inches be 

 added as the estimated surface of the bronchia, the 

 sum of the surface of the whole lungs in that animal 

 will be 41635 square inches, equal to nineteen times 

 the surface of a man's body, which is computed at 

 fifteen square feet {. Dr Keil estimates the diame- 

 ter of each cell in the human lungs at ~ part of an 

 inch, and its superficies at 0.01256: the whole 

 number of cells he calculates at 17,441,860, which, 

 multiplied by the superficies of each, makes the sum 



* Observations on the Animal (Economy, 2d edit. p. 134. 

 f Goodwyn's Essay, p. 58. 62. 

 | Statical Essays, vol. i. p. 241. 



