ANIMAL HEAT 521 



The surface temperature varies between rather wide limits with 

 the temperature of the environment. The temperature of cavities 

 like the rectum, vagina, and mouth, and of secretions like the urine, 

 approximates to that of the blood in the great vessels or the heart, 

 and undergoes only slight changes. An increase in the velocity of 

 the blood causes the internal and surface temperatures to come nearer 

 to each other, the former falling and the latter rising. When the loss 

 of heat from a portion of the surface is prevented, the temperature 

 of this portion approaches the internal temperature. For this reason 

 a thermometer placed in the axilla approximately measures the 

 internal temperature, and not that of the skin ; and a thermometer in 

 the groin of a rabbit, and completely covered by the flexed thigh, may 

 stand as high as, or, it is said, even higher than, a thermometer in 

 the rectum (Hale White). 



The surface temperature is a rough index of the rate of heat-loss ; 

 the internal temperature, of the rate of heat-production. A normal 

 skin temperature and a rising rectal temperature would probably indi- 

 cate increased production of heat; an increased rectal temperature, in 

 conjunction with a diminished surface temperature, as in the cold 

 stage of ague, might be due either to diminished heat-loss while the 

 heat-production remained normal, or to diminished heat-loss plus 

 increased heat-production. 



The following tables illustrate the differences of tempera- 

 ture found in the body. It should be remembered that the 

 numbers are not strictly comparable with each other; the 

 temperature of the mammals in which direct observations 

 have been made on the blood is not exactly the same as 

 that of man, the temperature of the dog, for example, being 

 a little (about i C.) higher. Then in the same animal there 

 is no very constant ratio between the temperature of the blood 

 in two vessels or of the skin at two points. Even in the 

 same vessel the temperature may vary with many circum- 

 stances, such as the velocity of the stream, and the state 

 of activity of the organ from which it comes. Apart from 

 physiological variations, experimental fallacies sometimes 

 cause a want of constancy, especially in measurements of 

 blood temperature. The insertion of a mercurial ther- 

 mometer into a vessel is very likely to obstruct the passage 

 of the blood ; and if the blood lingers in a warm organ, it 

 will be heated beyond the normal. 



