304 ANIMAL HEAT. 



ture of the body, the bulb of the thermometer should be inserted so 

 deeply as to pass beyond the superficial zone affected by the process of 

 external cooling. Even when placed beneath the tongue it is in contact 

 with parts which are themselves slightly cooled by the passage of the 

 air in inspiration and expiration, and accordingly does not reach the 

 maximum temperature of the body. To accomplish this, it must be in- 

 serted into the abdominal cavity or the rectum, so deeply that a further 

 introduction produces no increase in the indicated temperature. This 

 is the method usually adopted in physiological observations. 



Beside the differences observable from the above cause between the 

 superficial and the deep-seated parts, there is a real variation within 

 narrow limits of the internal temperature of the body, according to dif- 

 ferent physiological conditions. Jiirgensen has shown 1 that in the human 

 subject there is a diurnal variation, the temperature during the day 

 being a little higher than at night, even when both periods are passed 

 in complete repose. A series of observations upon the same individual 

 in a state of rest gave the following averages : 



TEMPEKATURE OF THE HUMAN BODY WHEN AT REST. 

 By day. By night. 



37.34 36.91 



The difference between the two averages amounts to 0.43. There 

 are also temporary variations of small extent during each of the above 

 periods ; the greatest variation during the day being 0.21 ; that during 

 the night 0.15. 



The temperature of the body is also increased by muscular activity. 

 It is a matter of common observation, both in man and animals, that 

 temporary exertion produces an increase of bodily warmth. Jurgensen 

 observed in the same individual that while during a day of absolute 

 rest the maximum temperature attained was 37.7, under the influence 

 of exercise it reached 38.8. A much more striking difference, corre- 

 sponding with muscular repose or activity, has already been mentioned 

 as observable in insects. 



The animal temperature is furthermore increased or diminished by a 

 condition of digestion or abstinence. This was indicated in several 

 instances by the observations of Jurgensen upon man, but is shown in 

 a very marked degree by those of Senator upon the dog, in which the 

 average production of heat was sensibly diminished by continued fast- 

 ing and increased by the digestion of food. The following table shows 

 the quantity of heat produced by the same animal, in the conditions of 

 abstinence and digestion. 



QUANTITY OF HEAT PRODUCED BY THE DOG IN ONE HOUR. 

 After two days' fasting .... 10.90 heat units. 

 After one day's fasting .... 12.63 

 Fed one hour previously .... 18.87 



1 Die Korperwarme des gesundcn Menscben. Leipzig, 1873. 



