142 NATURE AND LIFE. 



II. 



Independently of the slight and usual variations that 

 heat may present in the same species, and those it exhibits 

 in passing from one zoological group to another, we may 

 consider the changes it undergoes in the same individual, 

 influenced by the various disturbances of the system. Al- 

 though it remains almost insensible to modifications of the 

 surrounding temperature, it is not the same when the com- 

 plete equilibrium of the organs is affected. The concord 

 between the different parts of the organism and the func- 

 tions they discharge is so perfect that the least trouble is 

 reflected among them, and sends disorder everywhere. 

 The nervous system, charged with keeping up harmonious 

 communication between all points of the living being, first 

 takes note of the change befalling, and transmits its abnor- 

 mal impression into all quarters. It is not the generator, 

 but it is the regulator, of animal heat ; that is to say, it 

 directs and in a manner oversees its production and diffu- 

 sion according to the varying needs of the system. Every 

 lesion or affection of this system reacts on the physiologi- 

 cal processes, and particularly on the evolution of heat. 

 By cutting the filament of the great sympathetic nerve on 

 only one side of a rabbit's neck, Claude Bernard produced 

 an elevation of temperature of several degrees on that side. 

 The blood flows toward the point where the action of the 

 nervous system is suspended under any influence whatever, 

 bringing with it an increase of heating force. At a point 

 where the reverse occurs, the vessels contract, and the tem- 

 perature falls. 



Imperfect nutrition and fasting act on the animal heat, 

 but not directly. The organism keeps up to its normal 

 degree of temperature till it has exhausted its reserved 

 store of combustible substances. Then it cools slowly 

 down to a much lower degree. Thus, a rabbit, starved by 



