PREFACE. vii 



their operations with great method and design. This theory 

 was too loose, too indiscriminate, to engage long a serious 

 consideration. The fable of Prometheus shews that the in- 

 fluence of a living principle was esteemed necessary to the 

 phenomena of life: the theory of Stahl assigned every thing 

 to this principle : if it had assigned much, it would not have 

 greatly erred ; but in assigning any thing, it did not challenge 

 implicit belief, because it was a fancy, and not an induction ; 

 or because the inference was not supported by the sort of evi- 

 dence which philosophy requires. It strayed still further from 

 sober truth, by proposing an intelligent principle, when the 

 evidence upon the subject barely sanctioned the opinion of 

 the existence of a principle of any sort, distinct from the 

 material fabric. 



Very little has since been added to the theory of Stahl con- 

 cerning the general agency of a principle of life. The exist- 

 ence of the principle was insisted upon with some particularity 

 by Mr. Hunter : and it was said by him, as by Stahl, that this 

 principle was interested in all the operations of living bodies, 

 which is almost reverting to the fable of Prometheus ; for, if 

 the mechanism of a man could not perform the operations of a 

 Hying body, these operations must of course be attributed to 

 the principle without which they could not be performed. 

 The history of the affair thus far is simply this : the Anci- 

 ents supposed the phenomena of animal bodies to be performed 

 by a principle superadded to mechanism ; Stahl endowed this 

 principle with intelligence : Mr. Hunter adverts to the princi- 

 pie generally, as a principle of life, although in one function, 

 that of the absorbents, he appears to fall completely into the 

 theory of Stahl, by making these vessels little less than in- 

 telligent artificers. It is obvious that, up to this period, no 

 great progress has been made in developing the nature or laws 

 of the liring principle ; so loosely indeed has the subject al- 

 together been remarked upon, that the opinions of men are 

 itili divided, whether the phenomena of the living state are to 

 be referred to a principle of life, or whether they result merely 

 from the material fabric. 



