Chap. III. ACTION OF THE NERVOUS SYSTEM. 69 



be felt by the animal under experiment. Hence when 

 the mind is strongly excited, we might expect that it 

 would instantly affect in a direct manner the heart; 

 and this is universally acknowledged and felt to be the 

 case. Claude Bernard also repeatedly insists, and this 

 deserves especial notice, that when the heart is affected 

 it reacts on the brain; and the state of the brain again 

 reacts through the pneumo-gastric nerve on the heart; 

 so that under any excitement there will be much mu- 

 tual action and reaction between these, the two most 

 important organs of the body. 



The vaso-motor system, which regulates the diameter 

 of the small arteries, is directly acted on bv the sen- 



«/ «/ 



sorium, as we see when a man blushes from shame; but 

 in this latter case the checked transmission of nerve- 

 force to the vessels of the face can, I think, be partly 

 explained in a curious manner through habit. We shall 

 also be able to throw some light, though very little, on 

 the involuntary erection of the hair under the emotions 

 of terror and rage. The secretion of tears depends, no 

 doubt, on the connection of certain nerve-cells; but 

 here again we can trace some few of the steps by which 

 the flow of nerve-force through the requisite channels 

 has become habitual under certain emotions. 



A brief consideration of the outward signs of some of 

 the stronger sensations and emotions will best serve to 

 show us, although vaguely, in how complex a manner 

 the principle under consideration of the direct action 

 of the excited nervous system of the body, is combined 

 with the principle of habitually associated, serviceable 

 movements. 



When animals suffer from an agony of pain, they 

 generally writhe about with frightful contortions; and 

 those which habitually use their voices utter piercing 



