32 ON THE INFLUENCE 



duced, go far towards proving, that the tem- 

 perature of warm-blooded animals is considerably 

 under the influence of thenervous system. But 

 what is the nature of the connection between 

 them ? whether is the brain directly or indirectly 

 necessary to the production of heat ? These are 

 questions to which no answers can be given, 

 except such as are purely hypothetical. At 

 present we must be content with the knowledge 

 of the insulated fact : future observations may, 

 perhaps, enable us to refer it to some more 

 general principle. 



We have evidence, that when the brain ceases 

 to exercise its functions, although those of the 

 heart and lungs continue to be performed, the 

 animal loses the power of generating heat. It 

 would, however, be absurd to argue from this 

 fact, that the chemical changes of the blood in 

 the lungs are in no way necessary to the pro- 

 duction of heat, since we know, not only that 

 there is no instance in which it continues to take 

 place after respiration has ceased, but that re- 

 spiration is necessary to all the vital functions. 



hue ; but its natural colour may be restored by artificially 

 inflating the lungs, so as to furnish a greater supply of air 

 to the blood circulating through them. 



We may suppose that, on the division of these nerves, the 

 sympathy between the lungs and the nerves of inspiration is 

 either very much impaired, or altogether destroyed, so that 

 the animal does not experience the same impulse to draw in 

 fresh air as under ordinary circumstances. In consequence 

 his inspirations become less frequent than natural, and hence 

 arise the phenomena produced by this operation. 



