468 ANIMAL HEAT. [BOOK n. 



We may regard it then as established that such a thermotaxic 

 nervous mechanism does exist, and the importance of such a 

 mechanism in explaining not only the maintenance of the nor- 

 mal temperature but the abnormal variations of temperature in 

 disease can hardly be exaggerated. Much however still requires 

 to be learnt before we can speak with full confidence as to its 

 exact nature, or expound with certainty the details of its work. 



By regulative mechanisms of this kind the temperature of the 

 warm-blooded animal is maintained within very narrow limits. In 

 ordinary health the temperature of man varies between 36 and 

 38, the narrower limits being 36'25 and 37'5, when the thermo- 

 meter is placed in the axilla. In th?. mouth the reading of the 

 thermometer is somewhat ('25 to 1*5) higher; in the rectum it is 

 still higher (about *9) than in the mouth. The temperature of 

 infants and children is slightly higher and much more susceptible 

 of variation than that of adults, and after 40 years of age the 

 average maximum temperature (of health) is somewhat lower than 

 before that epoch. A diurnal variation, independent of food or 

 other circumstances, has been observed, the maximum ranging 

 from 9 A.M. to 6 P.M. and the minimum from 1 1 P.M. to 3 A.M. 

 Meals cause sometimes a slight elevation, sometimes a slight 

 depression, the direction of the influence depending on the nature 

 of the food : alcohol seems always to produce a fall. Exercise and 

 variations of external temperature, within ordinary limits, cause 

 very slight change, on account of the compensating influences 

 which have been discussed above. The rise from even active 

 exercise does not amount to 1 C. ; when labour is carried to 

 exhaustion a depression of temperature may be observed. In 

 travelling from very cold to very hot regions a variation of less 

 than a degree occurs, and the temperature of tropical inhabitants 

 is practically the same as of those dwelling in arctic regions. 



When external cold or warmth passes certain limits, or when 

 during the application of these agents the regulative mechanisms 

 are interfered with, the temperature of the body may be lowered 

 or raised until death ensues. When the cold or warmth applied is 

 not very great, as in cold and warm baths, it has been noticed that 

 the temperature is more easily raised by warmth than depressed 

 by cold. Death ensues from extreme cold by a depression of the 

 activities of all the tissues, more especially of the nervous; as- 

 phyxia is produced in animals when the fall of temperature is 

 rapid. Puppies can be recovered after the temperature in the 

 rectum has fallen to about 4 or 5 C., and hybernating mammals 

 may be cooled with impunity down to nearly freezing point. 

 When external warmth is brought to bear on a mammal in such a 

 way as to cause a rise of temperature in the body, death ensues 

 when an elevation of about 6 or 7 C. above the normal is reached. 

 The exact cause of the death has not been as yet sufficiently ex- 



