INTRODUCTION. 15 



formed their office, are become redundant, and, re- 

 assuming a liquid or gaseous form, traverse the 

 pores of the body, and are exhaled. The solids also 

 not only contain the liquids, but promote their 

 movement, by dilatation and contraction. 



But if this mutual action of the solids and liquids, 

 this change of atoms from one state to another, 

 really take place, it must follow that there is a close 

 affinity in the chemical composition of each; and 

 accordingly we find that such solids are in a great 

 measure composed of elements easily convertible 

 into liquids or gas *. 



tempted to be substituted, and after all with not the smallest success 

 in preventing a recurrence to this principle, of which all these proper- 

 ties, admitting their existence, are nothing- more or less than the re- 

 sults ; for however we may denominate them, we merely substitute 

 expressions, which (if they convey any meaning,) imply only the 

 existence of certain effects or operations, which proceeding from 

 a first cause, are inferior agents, or instruments, under the con- 

 trol of vitality, in the production of organic phenomena. 



* Yet no chemical combination or affinity, resulting from the 

 various proportions and conditions of the elements of matter, or of 

 their aggregate or more or less compound state with which we are 

 acquainted, can explain the changes of the circulating fluid into 

 organized solids, on the one hand, or the return of the animal 

 solids into the particular states of fluidity which they occasionally 

 assume in a living body, on the other. It is true that both the 

 solids and fluids of an organized body, in which life is extinct, may 

 be converted into other solids and fluids, by an abstraction, addi- 

 tion, or substitution of ingredients, or by such other change in 

 the elements which usually enter into their composition, to which 

 change these elements are naturally disposed, when that influence 

 is withdrawn which until then controlled their combinations and 

 forms of existence; but the products which thus result from the 

 spontaneous changes and chemical combinations, which take place 

 when the control of a superior principle is withheld, are altogether 



