86 



class of substances which appears to differ from the last, principally 

 in being of a more minute and intimate kind : they denote this class 

 by the term " affinity" 



36. Thus far the words attraction, affinity, &c. are applied 

 only to substances which possess all, or some of the properties by 

 which matter is recognized. But properties, not known as material 

 or falling under the classes of chymistry, are capable of modifying 

 each other (which is the best test of a perfect union among sub- 

 stances); and this is no more than we observe even of chymical sub- 

 stances, for in them properties modify each other, which are neither 

 tangible, visible, &c. nor endowed with any faculty, by which the 

 belief of a material presence is made to arise, as among unions of 

 the gaseous or other peculiar properties, which are superadded to 

 the material substances of chymistry. 



37. But, to avoid a cavil about words, we will not say that 

 these properties mix, unite, or combine; words that may be said to 

 apply only to things that are extended; but we will merely say what 

 we find to be the case, viz. that properties, different forms of 

 existence, may modify each other, and if the terms, " the union of 

 these properties, their combinations, &c." should be hereafter used, 

 it is now defined upon what conditions, and they must be allowed 

 to pass by favour, they being founded upon an analogy which in 

 some respects may be thought not unexceptionable. To return 

 then to our affinities. 



38. Among other relations, properties have one with matter, 

 by which matter tends to an union with properties: and this it may 

 do though already restrained by some power of union, provided the 

 last be the weakest, as we say. This law is illustrated by a thou- 

 sand instances in chymistry ; it is also illustrated by the phenomena 

 of magnetism ; it is also illustrated in animal processes, of which 

 one example will suffice. The living kidney produces urine from 

 the blood, while the dead kidney will not by any force of injection 

 of blood into its vessels, although its texture is preserved, and its 

 chymical constitution is not yet decomposed. In the animal de- 

 partment, I call the properties hinted at, for the sake of distinction, 

 spiritual properties, and their exertion in such instances an act 

 of affinity. 



39. The evidence of the resemblance of such an act of affinity 

 to those displayed in chymistry, is found not only in their apparent 

 analogy (with which alone we ought to be satisfied), but it is also 

 furnished a priori. The act in all instances is determined by 

 latent causes of union or separation, by which the relation is fixed. 

 These causes may differ, and the relation will be modified. Having 

 stated the grounds upon which the term affinity is employed, and 

 whal is meant by it, we are next to trace the processes which are 

 assigned to its agency. 



40. Fecundation, it has been said, disposes the properties of 

 the ovum to be active. These properties have been divided (at 14) 

 into three classes. This clarification was made, as comprehending 



