566 GENERATION. SECT. XXXIX. 4t 



7. All animals therefore, I contend, have a fimi- 

 lar caufe of their organization, originating from a 

 fingle living filament, endued indeed with different 

 kinds of irritabilities and fenfibilities, 'or of animal 

 appetencies ; which exift in every gland, and in 

 every moving organ of the body, and are as eflen- 

 tial to living organization as chemical affinities are 

 to certain combinations of inanimate matter. 



If I might be indulged to make a firnile in a phi- 

 lofophical work, I fhould fay, that the animal ap- 

 petencies are not only perhaps lefs numerous ori- 

 ginally than the chemical affinities ; but that like 

 thefe latter, they change with every new combina- 

 tion ; thus vital air and azote, when combined, 

 produce nitrous acid ; which now acquires the 

 property of diflblving filver ; fo with every new- 

 additional part to the embryon, as of the throat or 

 lungs, I fuppofe a new animal appetency to be pro- 

 duced. 



In this early formation of the embryon from the 

 irritabilities, fenfibilities, and affociabilities, and 

 confequent appetencies, the faculty of volition can 

 fcarcely be fuppofed to have had its birth. ; For 

 about what cannhe fetus deliberate, when it has not 

 choice of objects ? But in the more advanced flate 

 of the fetus, it evidently poffeffes volition ; as it 

 frequently changes its attitude, though it feems to 

 ileep the greateft part of its time; and afterwards 

 the power of volition contributes to change or alter 

 many parts of the body during its growth to man- 

 hood, by our early modes of exertion in the vari- 

 ous departments of life. All thefe faculties then 

 conftitute the vis fabricatrix, and the vis conferva- 

 trix, as well as the vis medicatrix of nature, fo 

 much fpoken of, but fo little underflood by philo-? 

 fophers. 



8. When we revolve in our minds, firft> the great 

 changes, which we fee naturally produced in ani- 

 mals 



