THE ESSENTIAL PHENOMENA OF RESPIRATION. 



13 



were found similar. Combustion is, indeed, the ulti- 

 mate object of the respiratory function. Oxygen is the 

 agent necessary for this combustion ; carbonic acid gas 

 and water vapor are the products resulting from the 

 combination of oxygen with the carbon and hydrogen 

 which enter into the composition of our tissues and the 

 fluids of our bodies. A candle, lamp, or gas flame that 

 burns in the air yields exactly the same products. 



FIG. 2. 



LUNGS AND HEART OP MAN. The left lung has been dissected so as to show 

 the interlacing of air-vessels and blood-vessels. P, right lung; Cs, upper 

 yena cava ; A, aorta ; Vd, right ventricle ; Ap, pulmonary artery ; Qd, right 

 auricle. 



Respiratory Apparatus. In man the respiratory ap- 

 paratus, strictly speaking, is the lungs, which are put in 



2 



