34 WONDERS OF ORGANIC LIFE. 



pints of air, in addition to ten or twelve pints 

 constantly in the vesicles. The blood is esti- 

 mated to perforin three complete circuits 

 through the body every eight minutes of time, 

 and the average quantity of blood in the body, 

 in health, is reckoned to be 384 ounces, or 

 twenty-four pounds avoirdupois, being nearly 

 twenty imperial pints. 



We have now to ascertain the result of the 

 action of the air upon the blood, and of the 

 blood upon the air ; and in following out this 

 subject we shall see how the laws of chemistry 

 are carried out, under the governance of a vital 

 principle. Oxygen is the great agent in ren- 

 dering the blood, whatever be the character of 

 that blood, fitted for the purposes of the animal 

 economy. No animal, whether it respires air 

 or water, whether it is furnished with lungs or 

 gills, or vibratile cilia, or whether the external 

 surface alone acts as a respiratory organ, can 

 live, unless a certain portion of oxygen be 

 present in the fluid, whether air or water, which 

 it respires. Every other gas in a pure state, 

 such as azote or nitrogen, and hydrogen, and 

 also carbonic acid gas, soon destroys the life of 

 an animal forced by way of experiment to inhale 

 it. Pure oxygen alone, although it will support 

 life for a considerable period, is, when unmixed, 

 too great a stimulant, and tends to exhaust the 

 vital energies ; oxygen must be diluted with 

 azote ; and t of such is the atmosphere of our 

 globe composed, with certain non-essentials, as 

 carbonic acid, vapour, and exhalations from 



