I#^ THE PHILOSOrHY 



iflitnent, neceHarlly excite defu*e or appetite. But, if a man 

 be deprived of feofation, want cannot exiH:, becaufe all its 

 fources are annihilated. This is cutting off all the caufes, 

 and at the fame time looking for the effejTcs. An animal 

 witnout fome fenfation is no animal, but a dead mafs of mat- 

 ter. Sentiment is the only flimulus to animal motion •, the 

 aptnefs of the parts produces the cfFeft, which varies accord^ 

 ing to the ftruflure and deftination of thefe parts. The 

 fenfe of want creates defire. Whenever an animal perceives 

 an obje(St fitted to fupply its wants, delire is the neceffary 

 €onfequence, and action or motion inftantly fucceeds. 



Belide progreffive motion, the motion of hands, and other 

 parts of animal bodies, which are all effected by means of 

 mufcles, and are fubjeft to the will of the creatures who per- 

 form them, there are other motions that have little or no 

 dependence on our inclinations. Of this kind are the a6lion 

 of the heart, the circulation of the blood, the digeftion of 

 food, the periftaltic motion of the bowels, the progrefs of 

 the chyle from the ftomach and inteftines to the fubclavian 

 vein, the movement of the various fecreted liquors, llich as 

 the gall, the urine, the faliva, &c. Thefe, together with the 

 a6tion of the lungs in refpiration, have received the denomi- 

 nation of vital and invohmlary motions^ becaufe m.oll: of them 

 go on without any confcious exertions of the intelleclual 

 principle. If fuch a variety of nice and complicated move- 

 ments had been left to the determination and dire<51:ion of 

 our minds, they mud neceffarily have occupied too much of 

 our attention j and many of them would infallibly have been 

 negle£led during fleep, wheri confcioufnefs is often tilmofi: 

 totally fufpended. But Nature in her operations is always 

 wife. She has given to man, and other animals, the direc- 

 tion of no movements but what are eafily performed, con- 

 tribute to pleafure and health, and enable them to acquire 

 food correfponding to the ftruclure of their bodies and the 

 €\ements in which they live. 



