AND ANIMAL LIFE. 18 



inches, " so as to give 200 or 210 cubic inches 

 as the difference between the states of ordinary 

 inspiration and of forced or extraordinary ex- 

 piration."* As it is impossible to empty the 

 lungs completely, many calculations have been 

 made concerning the quantity of the residual 

 air which must necessarily remain after violent 

 or long continued expirations ; and this most 

 probably amount to 120 cubic inches.t From 

 the above statement, it is clear that, after an 

 ordinary expiration, 280 or 290 cubic inches re- 

 main in the lungs, in other words, 7 or 7^ of 

 ordinary inspirations. What is the intention of 

 Nature in giving to the lungs a capacity suf- 

 ficient to contain almost 300 cubic inches of air 

 after the evolution of that portion which is no 

 longer fit for the animal economy ? The ex- 

 planation of this intention will throw new light 

 on many mysterious changes of the system. 



XIX. The air which is received by any single 

 inspiration, does not immediately act upon the 

 blood ; its office is to supply the deficiency oc- 

 casioned by the previous expiration ; and after 

 several series of such expirations it is then brought 

 into intimate contact with this fluid, and tends to 

 continue the successive alterations which it un- 

 dergoes. 



XX. The organization of the lungs allows a 



* BOSTOCK'S Elementary System of Physiology, Vol. ii. p. 25. 

 f .Ibid, p 29. 



