ANIMAL HEAT. 175 



CHAPTER X. 



OF ANIMAL HEAT. 



Participation of Organic Forms in external Variations of Temperature. Mechanism for counter* 

 balancing these Variations. Development of Heat in Plants at Germination and Inflorescence. 

 Its Cause is Oxidation. Connection of Respiration and Heat. Temperature of Man. His 

 Power of Resistance. The diurnal Variations of Heat. Connection of these Variations with 

 organic Periodicities. Annual Variations of Heat. Control over them by Food, Clothing, and 

 Shelter. Source of Animal Heat. Effect of Variations in the Food and in the respired Me- 

 dium, both as respects its Nature and Rarefaction. Hybernation. Starvation. Artificial Re- 

 duction of Temperature by Blood-letting. Principles of Reduction of Temperature. Radia- 

 tion. Contact. Evaporation. Their Balance with the Heating Processes. Local Varia- 

 tions eliminated by the Circulation. Control by the Nervous System. Its physical Nature. 

 Allotropism of Organic Bodies. 



OWING to the earth's diurnal rotation on its axis, and its annual move- 

 ment of translation round the sun in an orbit inclined to the , 7 . 



Variations of 



equator, variations of temperature arise, the vicissitudes of external tem- 

 summer and winter, day and night. perature. 



In these variations all objects upon the surface of the planet partici- 

 pate ; organic forms are no exception. As the heat of the medium in 

 which they live ascends or descends, theirs follows it at a rate depend- 

 ent on their conductibility. 



Like mineral substances, the more lowly forms of life submit to these 

 changes. They have no provision for check or compensation. Organic forms 

 In summer, the temperature of the stem of a tree rises with- t^ ^-^. 111 

 out any restraint; in winter it declines; and, should the tions. 

 point be reached at which those nutritive changes that give motion to the 

 sap cease, nothing is done to arrest the descent, and the whole organism 

 passes into a state of torpor, hybernation, or temporary death. 



Now, since this following of atmospheric temperatures must take place 

 in every organism as well as in every mineral body, the con- Compensating 

 struction of one having a uniform mode of existence in all 

 climates and all seasons implies a resort to some subsidiary tribes. 

 mechanism, which, though it may not check, may yet compensate for 

 these vicissitudes. Accordingly, so nearly is this equalization accom- 

 plished in the highly-developed tribes, and a standard temperature so 

 nearly attained for them, that many physiologists, misled by imperfect 

 observations, have concluded that such living beings are emancipated by 

 nature from the operation of physical laws : an erroneous conclusion, for 

 in them that action is only concealed. 



