34 



Example of exception : the prick of a pin will produce pa in ; so will 

 that of a needle, so will hot water, or caustic, or an incision with a 

 knife, with a razor, or a scythe; all these things produce pain: all 

 these things are causes, yet they are not the same. But have they 

 no relation with sensibility which is common to them all ? Why 

 truly they must: and for this reason, viz. that pain can be identified 

 only by its causes. Those causes must be operative which can 

 make pain: if they are not these causes, if they are more or less, 

 they will make something else corresponding with ivhat they are, 

 and not pain ; or else such a modification of pain, as will agree with 

 the diversity of the real causes. If, therefore, the causes are diffe- 

 rent, the effect also will be different, or those which we suppose to 

 be causes are none. 



76. To take another example: a ligature on a nervous trunk 

 will paralyze the parts to which its branches are distributed. This 

 effect will be produced by thread, by silk, by cotton, by a piece of 

 whipcord or catgut, or horse-hair; by pinching the nerve between 

 the finger and thumb, by applying a red-hot wire to it, by dividing 

 it with a knife. These causes, as they are called, in the gross, are 

 all very different, yet the effect is the same; and. why? It is, that 

 they possess in common one relation ; or, that the real cause, that 

 which is productive of the effect, is the same in them all : the other 

 appearances, properties, &c. which identify these nominal causes, 

 and distinguish them from each other, are mere associations, or 

 adjuncts, which do not produce the effect, having no relation with 

 the subject of the influence, although connected with a real cause. 

 And what is this common relation? Why, the ligatures, whether of 

 hair, or silk, or catgut, &c. having in common a certain figure, a 

 certain tenacity and strength, which admit their being drawn tight, 

 and thus making a certain degree of pressure, are capable, each, by 

 these properties, which are common to all, of compressing the 

 theca of the nerve, and of displacing a circle of the medulla : this is 

 their share in the effect ; the phenomena are then left to other causes ; 

 and the relation afterwards is, that no nervous influence is com- 

 municated beyond a place in the nerve so circumstanced. But 

 what shall we say of the knife, which is different from all the 

 ligatures? The knife produces one effect in common with the 

 ligatures; and as it is a different cause, or as different causes act, it 

 produces other effects which the ligatures do not. By it the nerve 

 is divided what follows? The law with respect to the function of 

 the nerve is, that it requires a perfect continuity of the entire 

 structure of the chord. Is not this continuity interrupted in both 

 instances, is not this the common effect? or the common relation 

 in which all these agents stand with respect to the nerve, and the 

 phenomena of their application ? It must be allowed that it is: and 

 the same does obtain, must obtain, if there is any truth in our first 

 principle, in all instances. This confusion of real causes with their 

 connected properties is a great stumbling-block in matters of 

 science: but as the principle has never been reconciled and ex- 



