178 ANIMAL-SENTIENT FORCES. [i. 



Actions of Intellectual Pleasure and Pain through the Nerves 

 on the Mechanical Machines. 



333. The pleasure and pain which are connected with the 

 intellectual conceptions^ and render them motives to action, act 

 in virtue of their impressions in the brain (121, 80) on the 

 the vital movements, which are changed in proportion to the 

 strength of the impressions (250, 251). It is a well-known 

 and undoubted fact, that deep thought on abstract subjects 

 causes a manifest change in the circulation of the blood ; the 

 extremities become cold, while contrarily the vessels of the 

 head are filled, so that they beat more powerfully, and cause 

 redness and heat of the face, swelling of the head, headache, 

 perspiration on the forehead. Of the changes mentioned, those 

 which are most contra-natural are observed principally when 

 the thoughts are unpleasing, but even the pleasing may excite 

 such, if they be excessive. If a pleasing meditation be not 

 too deep, it excites only a vivid colour in the cheeks, and 

 favours the transpiration from the head ; a deep meditation on 

 painful subjects, on the contrary, causes vertigo, strong pulsa- 

 tion of the vessels, and a profuse perspiration, so that it is said 

 the head smokes. But since sensational stimuli accompany all 

 motives, and therefore all intellectual pleasure and pain (251), 

 it is not easy to determine, whether this operation of the 

 motives depends specially on intellectual pleasure and pain, or 

 on the accompanying sensational stimuli (252). Still the dif- 

 ference between the changed vital movements of deep thought 

 and those of sensational stimuli is so great, as to induce us to 

 doubt, whether they both spring from the same source. The 

 determination of the blood to the head, in operations of the 

 understanding, is not like that resulting from sensational stimuli, 

 for the blush of shame, and the violent derivation of the blood 

 to the head in anger, and in other instincts and passions, are 

 changes in the circulation of quite a different kind. Besides 

 these operations of the motives are weaker than those of the 

 sensational stimuli (250), and have this peculiarity, that they are 

 not excited either directly or proximately by external sensational 

 out according to the laws of the intellect (110). The intel- 

 lectual conceptions please or displease, according as they are 

 considered to be good or bad; the sensational conceptions 



