24 OF THE VITAL POWERS. 



acquires in the lungs from the air a certain principle to 

 be universally distributed during circulation, for the 

 purpose of imparting motion, &c. to the organs, were 

 right, if they regarded that principle (analogous to the 

 oxygen of the moderns) as the stimulant of the living 

 solid ; wrong, if they regarded it as vitality itself. 



51. For it is on all hands agreed, that no motion oc- 

 curs but upon the action of stimuli, to receive which 

 action the vital powers are naturally adapted and 

 intended. 



52. These stimuli, * however multifarious, are conve- 

 niently reduced to three classes; — chemical, mechanical, 

 and mental. For the present, we shall say nothing of 

 their various modes of action, — in some instances 

 direct, — in others indirect, by sympathy and sensorial 

 reaction. It is sufficient at present to cite a few ex- 

 amples of functions, to which, each class of stimuli 

 conspires; such is the increased secretion of tears, 

 saliva, bile, &c. and the venereal turgescence of the 

 genitals. 



53. If the nature of stimuli is infinitely various, no 

 less so are their effects, according to their nature, inten- 

 sity, or continued and repeated application to the living 

 solid. Hence they are generally divided into exciting 

 and depressing. 



54. The power of certain stimuli in increasing the 

 ^____ 



" Respiration supplies a very subtle air, which, when intimately mixed with 

 the blood, greatly condensed, conveyed to the moving fibres, and allowed by 

 the animal spirits to exert its powers, inflates, contracts, and moves the muscles 

 and thus promotes the circulation of fluids and imparts motion to mobile 

 parts." 



♦ Laur. Bellini, De Sanfptinit Musione. p. 165 — 193. 

 Sylvest Douglas, De Stinuilis. Lugd. Bat 1766. 



