Defence of the Doctrine of Vital Affinity. 341 



Dr Daubeny, that there appears to be a " power, residing in living 

 matters" and producing chemical effects, — in fact manifesting itself 

 most unequivocally by the chemical changes which result from it, — 

 " distinct, at least in its effects, from ordinary chemical and physical 

 forces." 



But after having made this statement, Dr Daubeny, according to the 

 author of this paper, has thrown a degree of mystery over the subject 

 which is quite unnecessary and even unphilosophical, by refusing 

 to admit — and quoting Humboldt, who has changed his opinion on 

 the subject, and now likewise declines to admit — that these changes 

 are to be regarded as vital ; both authors (as well as several other 

 recent English authors) maintaining, that as we do not know all the 

 conditions under which ordinary chemical affinities act in living 

 bodies, we are not entitled to assert that these affinities may not yet 

 be found adequate to the production of all the chemical changes 

 which living bodies present ; and that until this negative proposition 

 is proved, it is unphilosophical and delusive to suppose the existence of 

 any such power, as that to which the term Vital Affinity has been 

 applied by the author of this paper and several other physiologists. 



In answer to this, it is here stated, that as we cannot strictly speak- 

 ing, define Life or Vitality, we follow the strict rules of philosophy, in 

 describing what we call living bodies, whether vegetable or animal, and 

 then applying the term Vital or living, as the general expression for 

 everything which is observed to take place only in them, and which 

 is inexplicable by the physical laws, deduced from the observation 

 of the other phenomena of nature ; that according to this, — the only 

 definition of which the term vital admits, or by which the objects of 

 Physiology can be defined, — Dr Daubeny has already admitted, in 

 the expressions above quoted from him, that chemical as well as me- 

 chanical changes in living bodies, fall under the denomination vital ; 

 and as the rule of sound logic is *' afirmantibus incumbit pro- 

 batio," — and as it is just as probable ct priori, that, with a view 

 to the great objects of the introduction of living beings upon earth, 

 the laws of chemistry, as those of mechanics, should be modified or 

 suspended by Almighty Power, — this author maintains that we are 

 as fully justified in referring all great essential chemical phenomena, 

 which are peculiar to living bodies, to peculiar affinities, which we 

 term vital, as Haller was to ascribe the peculiar mechanical move- 

 ments of living bodies to the vital property of Irritability ; and to 

 throw on the mechanical physiologists of his day the burden of prov- 

 ing, if they could, that the laws of motion, perceived in dead matter, 

 were adequate to explain them. 



In illustration of the importance, both in Physiology and Patho- 

 logy, of this principle being held to be established, Dr Alison ad- 

 duced two examples, first, the utter failure of the very ingenious 

 theory of Dr Murray to explain, on ordinary chemical principles, 

 the simplest and most essential phenomena of healthy Secretion ; and, 



