176 THE LAWS OF ORGANIC 



fluid, thereby enabling the inspired air to oxy- 

 genate more completely the diminished propor- 

 tion which remains ; or, if he be exposed to ex- 

 ternal heat, precisely the same consequences fol- 

 low. The surface of the body is stimulated and 

 the blood flows to its minute vessels in greater 

 quantity and velocity than usual ; and in this way 

 the lungs and heart are quickly excited, the re- 

 sult of which is that they co-operate with the ex- 

 ternal heat in maintaining the diffused condition 

 of the circulation, and in promoting the same 

 physical phenomena. 



CXCV. If the external heat be very great, 

 the same effects become more apparent ; because 

 the quantity of blood transmitted through the 

 lungs at any one moment diminishes in the in- 

 creasing ratio of the temperature. In xvm. 

 xix. and xx. I explained why animal heat is not 

 in the direct ratio to the quantity of oxygen inhaled, 

 but in the inverse ratio to the quantity of blood ex- 

 posed to this principle. In extending the same 

 view, we shall understand why the system is ca- 

 pable of resisting a temperature of from 240 to 

 260, which was experienced by BLAGDEN. 



CXCV I. After an ordinary expiration, the 

 quantity of air remaining in the lungs is estimat- 

 ed at 280 or 290 cubic inches; but if the tempera- 

 ture of the body be increased from 5 to 10 more, 

 the air will be much rarefied, and, consequently, 

 the same quantity will not continue to act upon 



