256 SENSATION AND THE SENSIFEROUS ORGANS. 



problems. In fact, the sensory operations have been, 

 from time immemorial, the battle-ground of philosophers. 

 I have more than once taken occasion to point out 

 that we are indebted to Descartes, who happened to be a 

 physiologist as well as a philosopher, for the first distinct 

 enunciation of the essential elements of the true theory 

 of sensation. In later times, it is not to the works of the 

 philosophers, if Hartley and James Mill are excepted, 

 but to those of the physiologists, that we must turn for 

 an adequate account of the sensory process, nailer's 

 luminous, though summary, account of sensation in his 

 admirable "Prirnae Lineae," the first edition of which 

 was printed in 1747, offers a striking contrast to the 

 prolixity and confusion of thought which pervade Reid's 

 " Inquiry," of seventeen years' later date.* Even Sir 

 "William Hamilton, learned historian and acute critic as 

 he was, not only failed to apprehend the philosophical 

 bearing of long-established physiological truths ; but, 

 when he affirmed that there is no reason to deny that the 

 mind feels at the finger points, and none to assert that 

 the brain is the sole organ of thought,f he showed that 



* In justice to Reid, however, it should be stated that the chapters on 

 sensation in the " Essays on the Intellectual Powers " (1785) exhibit a great 

 improvement. lie is, in fact, in advance of his commentator, as the note 

 to Essay II. chap. ii. p. 248 of Hamilton's edition shows. 



f Haller, amplifying Descartes, writes in the " Prirnae Lineae," CCCLXVI. 

 " Non est adeo obscurum sensum omnem oriri ab objecti sensibilis im- 

 pressione in nervum quemcumque corporis humani, et eamdem per eum 

 nervum ad cerebrum pervenientem tune demum representari animse, quando 

 cerebrum adtigit. Ut etiam hoc falsum sit animam inproximo per sensoria 

 nervorumque ramos sentire." . . . DLYII. " Dum ergo sentimus quinque 

 diversissima entia conjunguntur: corpus quod sentimus: organ! sensorii 



