,164 



8. The place of injury, or that which appears to- give origin 

 to the series, may be called the primary seat; that place, or those 

 spheres, where the distant or contiguous effects of the injury are 

 contemplated, may be called the secondary seat, which may also 

 be the primary in relation to a further seat of affection, and so on 

 to an undefined extent. 



9. In our doctrines of causation we have assigned only two 

 modes of influence producing change, viz. by adding to or taking 

 away from the properties which constitute the subject of the 

 influence, or the subject of the change. When the function of 

 uninjured parts of the brain cease (as they will) from an injury of 

 the spinal marrow, what, according to the investigation just pro- 

 posed, is the process of this consequence! The brain was in 

 possession of certain faculties, which were manifested by their 

 operation: the spinal marrow is injured, and those faculties of the 

 brain cease,' or reverse the order, and suppose the function of the 

 spinal marrow to cease from an injury of the brain; this case is 

 not so liable to objection, by reason that though an universal 

 paralysis may have occurred in the system of voluntary motion, &c. 

 yet the action of the heart may be but slightly interrupted. A 

 change has taken place in a secondary seat: has it arisen from a 

 communication of properties to it from the primary, or seat of the 

 injury? or, is it that the natural functions of the secondary, was 

 before dependent upon properties imparted to it from the primary, 

 eat, which communication of properties ceasing in consequence of 

 the injury, the dependent function of the secondary seat ceases 

 from their privation? This question, which is in every respect a 

 legitimate one, shakes some received doctrines of physiology to 

 their foundation. 



10. There are many parallel cases where the question is also, 

 though perhaps not equally, applicable. A nerve is intercepted 

 and the functions of the inferior parts cease. Hence it is inferred 

 that the inferior parts were in a sort of habitual receipt of proper- 

 ties or faculties from the superior parts. This inference is made 

 upon an analogy which must not be universally admitted: it must 

 not be admitted (unless it should be found to agree with a criterion 

 which remains to be discovered), because in the instance of a nerve 

 the properties of it might be, in a way before explained, related 

 with the foreign agency. Not so with the blood in an artery, 

 which is a specimen or the analogy : here the communication is 

 merely cut off; out in a nerve the properties of inferior parts may 

 be modified or destroyed by an influence conferred. I would ask, 

 theft, as the effects of injuries of this kind may happen in two ways, 

 what known criterion have we by which to ascertain from such ex- 

 periments the true relation between connected parts? 



11. This criterion can neither be deduced from succession 

 nor from the existence or want of reciprocation; to exemplify, it 

 may be said the destruction of the function of the lower portion of 

 a nerve always succeeds to its division, while the superior portion? 



