12 THE LAWS OF ORGANIC 



cubic inches of air, the whole internal surfaces 

 of the lungs will be nearly equal to 440 square feet, 

 or nearly thirty times greater than that of the 

 whole external surface of the body." * 



From the little already stated concerning the 

 action of inspiration and expiration, it is manifest 

 that the proportion of blood and air is subject 

 to great variations ; and it is my intention to 

 explain more particularly the nature and origin 

 of these. 



XVII. It is not easy to ascertain the quantity 

 of air which is evolved at each ordinary expira- 

 tion ; this is so materially modified by the state 

 of the mind, system, and capacity of the chest, 

 that great discrepancies unavoidably exist in the 

 results of the most distinguished chemists. But 

 the data which I shall presume to establish, and the 

 reasoning which will naturally flow from them, 

 will be little affected by the varieties of opinion. 



Dr BOSTOCK has paid considerable attention 

 to the subject of respiration, and his contribu- 

 tions are neither few nor unimportant ; and, on 

 this account, I shall draw my deductions from 

 the experiments of this talented individual. 



XVIII. By an ordinary expiration, 40 cu- 

 bic inches of air are emitted ; but after this we 

 are enabled to expel a considerable portion, and 

 this quantity is estimated at 160 or 170 cubic 



* MONRO'S Elements of Anatomy, Vol. ii. p. 95. 



