CHAPTER XII. 



ANIMAL HEAT. 



ONE of the most important results of the metabolism of the tissues is 

 the production of the heat of the body. It is by this means that the 

 bodily temperature is raised to such a point as to make life possible. 

 In man and in such animals as are called warm-blooded, including only 

 mammals and birds, it is found on the one hand, that there is an aver- 

 age temperature which is maintained with only slight variations in spite 

 of changes in their environment, and on the other hand, that the pos- 

 sible variations above and below this average are comparatively slight. 

 It must not be thought, however, that the average temperature in all 

 mammals and birds is the same; for example, as we shall see. the average 

 temperature of man is just 37 C. (98.6 F.), in some birds it is as high 

 as 44 C. (111 F.), whereas in the wolf it is said to bennder 36 

 (96 F.). 



The average temperature of the human body in those internal parts 

 which are most easily accessible, as the mouth and rectum, is from 36.9 

 -37.4 C. (98.5 to 99.5 F.). In different parts of theexternal surface 

 of the human body the temperature varies only to the extent of one or 

 two degrees (C.), when all are alike protected from cooling influences; 

 and the difference which under these circumstances exists, depends chiefly 

 upon the different degrees of blood-supply. In the axilla the most 

 convenient situation, under ordinary circumstances, for examination by 

 the thermometer the average temperature is 36.9 C. (98.6 F.). In 

 different internal parts, the variation is one or two degrees; those parts 

 and organs being warmest which contain most blood, and in which there 

 occurs the greatest amount of chemical change, e.g., the muscles and 

 the glands; and the temperature is highest, when they are in a condi- 

 tion of activity: while those tissues which, subserving only a mechanical 

 function, are the seat of least active circulation and chemical change, 

 are the coolest. These differences of temperature, however, are actually 

 but slight, on account of the provisions which exist for maintaining 

 uniformity of temperature in different parts. 



Circumstances causing Variations in Temperature. The chief circumstances 

 by which the temperature of a healthy body is influenced are the following : 



Age. The average temperature of the new-born child is only about half a 

 degree C. (1 F.) above that of the adult; and the uitference becomees still 

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