1096 ANIMAL HEAT 



ing. In animals an extreme drop in their body-temperature may be 

 produced by exposing them to cold air or water. Owing to the reduc- 

 tion in the warmth of the tissues then ensuing, the nerve centers soon 

 lose their irritability, which condition in turn gives rise to paralyses 

 of motion and sensation. While it is difficult to give a precise lower 

 limit, recovery has been noted in persons whose body-temperature had 

 been reduced to 24 C. 



As far as the minor fluctuations are concerned, it should be noted 

 first that the body-temperature of children is higher than that of adults, 

 amounting to 37.8 C. at birth and to 36.8 C. shortly afterward. 

 Within the succeeding 24 hours, however, the heat-regulatory mech- 

 anism becomes functional and the temperature rises to 37.5 C. 

 Between puberty and the age of forty it remains at 37.1 C. A slow 

 decline then sets in until about the seventieth year, when it again rises. 

 The diurnal variations in the body- temperature are closely allied to 

 the changes in the intensity of the metabolism, being lowest at about 

 5 o'clock in the morning and highest at about 6 or 7 o'clock in the 

 evening. Besides, they may be greatly modified by the occupation 

 of the individual. Thus, they are commonly reversed in persons 

 who follow their vocation at night and sleep during the day. After 

 meals the body-temperature is somewhat higher than normal, owing to 

 the increased glandular activity and peristalsis, as well as to the heat 

 liberated by the food. Iced drinks and cold food, on the other hand, 

 abstract heat from the body and tend, therefore, to cause a slight 

 reduction, if used in large amounts. An insufficient intake of food 

 lowers the temperature because it tends to lessen metabolism. Any 

 one of these changes, however, rarely amounts to more than 0.2 or 

 0.3 C. and does not last long. 



It is a matter of common experience that muscular exercise affects 

 the body-temperature in a very decisive manner. Thus, even such 

 relatively slight efforts as are required to play a game of tennis, suffice 

 to raise it a degree or two above normal, but inasmuch as this activity 

 invariably increases the bloodflow, this superfluous amount of heat is 

 soon dissipated. During the summer, the mean body-temperature 

 exceeds the normal by as much as 0.5 'C., and even the ordinary 

 changes in the outside temperature occurring in the course of a day, 

 may vary the body-temperature by several tenths of a degree. Much 

 more decisive changes follow the immersion of the body in warm or 

 cold water. 1 Those mammals which at the approach of winter enter 

 the state of hibernation, suffer a constant loss of heat until their 

 temperature has reached a level only slightly above that of the sur- 

 rounding atmosphere. Evidently, this effect depends in large part 

 upon a lessened heat-production brought about by a reduction in 

 their bodily activities. Upon awakening in the spring, their tempera- 

 ture frequently mounts very rapidly in complete correspondence with 

 the rather sudden resumption of their active life. Drugs affect the 



1 Dill, British Med. Jour., 1890. 



