INTERNAL TEMPERATURE. 149 



where it is exposed to the inhaled air, and when it reaches the 

 arteries it is slightly colder than it was when in the right 

 side of the heart, although it is not quite so cold as the blood 

 in the jugular vein. That the blood should be cooled in passing 

 through the lungs is contrary to all old beliefs, but it will 

 not strike the student as strange when he considers how much 

 heat is abstracted by the inhaled air before it quits the lungs. 

 The absorption of oxygen by venous blood is proved experi- 

 mentally to be accompanied with a certain evolution of heat ; 

 but the quantity is not sufficient to balance the loss by ex- 

 posure to air inhaled at ordinary temperatures. 



In disease, the temperature of the body may vary greatly 

 from the healthy standard ; in febrile affections it may rise 

 to 106 or more, and in conditions of great feebleness, such 

 as the collapse in cholera, it has been known to descend 

 below 70. 



It will be understood, however, that the extremes of ex- 

 ternal temperature, which can be borne with impunity, are 

 not accompanied with any such changes within the body, but 

 illustrate the power which the body has of maintaining its 

 own proper temperature. Thus, in extreme cold, the greater 

 combustion necessary in the tissues is testified by the more 

 active respiration; while in exposure to heat, the body is kept 

 cool by evaporation. Temperatures far above what would 

 be sufficient to boil the juices of the body, were they exposed 

 directly to the heat, can be borne for a short time with 

 impunity, provided always that the air be dry, so as to aid 

 free evaporation from the surface ; but moist air cannot be 

 endured above a very moderate heat. 



