142 NATURE AND LIFE. 
Il. 
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 thesystem. 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. Ata 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 
