1903.] on The Paths of Volition. 269 



the solution of geometrical problems — a discovery which was made at 

 the age of 23. Quitting the army in 1621 he travelled in various 

 parts of Europe for a time, and presently found his way again to Paris, 

 where he made acquaintance with many of the prominent literary and 

 scientific men of the day. France, however, was not a safe place to 

 reside in for anyone who was inclined to be speculative in the regions 

 of science and metaphysics. He accordingly made ujd his mind to 

 settle in Holland, and in 1625 he proceeded thither and resided there 

 for nearly 20 years. It was here that he published eventually his 

 famous ' Dissertatio de Methodo,' as well as a series of essays em- 

 bracing metaphysics and nearly all the natural sciences. Having 

 acquired some knowledge of anatomy he began to formulate original 

 ideas on the subject of human physiology, which were published 

 (with other essays on metajDhysics and physics) in au essay which is 

 contained in the ancient tome upon the table before me, the title- 

 page of which I show you in the lantern. It was in this essay that 

 he set forth his conception of the nervous system. The brain had 

 long been recognised as the seat of intelligence ; Descartes proceeded 

 to further localisation, considering one particular spot in the centre 

 of the brain, the conariura or pineal gland, to be more especially 

 the seat of the soul. He v/as acquainted with the fact that through 

 the spinal marrow, and the nerves issuing from it, the brain was 

 brought into connection with sensory surfaces and with muscles, and 

 he formulated a scheme of the manner in which a sensory impression 

 may be transformed into movement. Looking upon the nerves as 

 tubular cords, along which might flow that entity to which the older 

 writers applied the term " animal spirits " — and which we in these 

 modern times, without really knowing anything more about it than 

 they did, now speak of as " nervous impulses " — Descartes supposed 

 that they (the nerves) might possess some kind of valvular arrange- 

 ment by which the animal spirits are directed into this or that 

 channel, with the view of producing this or that movement; in a 

 modified form this supposition has been revived in modern physio- 

 logy. As is plain from the diagrams which I here show you, he 

 clearly conceived that when a voluntary movement is performed 

 it is the result of impulses which are carried to the brain along 

 sensory nerves, and which, being transferred within the brain 

 along motor paths, cause such movement. He explains, in the page 

 here produced, how contact with the fire. A, produces an efi"ect which 

 is propagated along the nervous cord, C i^ which he compares to the 

 cord of a bell), so that instantaneously at the other end of the cord 

 an effect is produced, at the seat of intelligence, of such a nature that 

 the "animal spirits," or "nervous impulses," are made to jmss by 

 appropriate nervous channels so as to cause such a movement as to 

 fend off the fire. Descartes did not clearly distinguish — this was 

 not indeed done until nearly two and a half centuries later — between 

 what is commonly spoken of as a reflex action (not necessarily 

 accompanied by consciousness) and volitional action which we are 



