118 DR seller's memoir OF THE 



takes effect on appointed motor-cells in the cerebro-spinal axis, through vertical 

 internuncial threads in that axis. Whence arises a question for investigation, 

 whether each contractile fibre has a cell in the cerebro-spinal axis appropriated 

 to itself, and whether the same cell determines the contraction of that fibre in the 

 case in which the exciting influence is conveyed by a horizontal internuncial 

 thread, as well as when conveyed by a vertical internuncial thread. To this 

 may be joined another question ; namely, whether, when the same contractile fibre 

 is acted on by volition, the effect be produced through the same cell and the same 

 vertical internuncial thread. 



Volition is plainly of the same character when exercised over thoughts as 

 when exercised over impulses to muscular contraction. It has no direct power 

 over either ; but by frequent exercise it can command both with a great degree 

 of certainty. If a thought has been once present to the mind, and has received 

 a certain amount of attention, it belongs to the memory, and may usually be 

 recalled when required. So the consciousness of the contraction of a muscular 

 fibre, by attention, becomes an object of memor3^ When it is recalled, the effect 

 of the act by whicli it was before produced is recalled also. In this manner voli- 

 tion plainly extends its power over the muscular frame in such acquired efforts 

 as skating, tight-rope dancing, and the exhibitions of the slack-wire. But it is 

 not improbable that the memory of the consciousness attendant on the automatic 

 contraction of a muscular fibre in the early period of life, is the source whence 

 volition derives its first power over the muscular system. The consciousness 

 attendant on the contraction of a set of muscular fibres must be the same, 

 whether the act be automatic or the effect of volition. Whence the remembrance 

 of the consciousness must be the same, from whichever source derived. But if 

 the remembrance of an act determined by volition be the condition on which it 

 can be repeated, the remembrance of an automatic act should be sufficient to pro- 

 duce that act, even though it had never before occurred under volition. Volition 

 is commonly represented as conative, or attended with a particular effort ; but 

 if it simply exert an influence on the motor cells of the cranio-spinal axis con- 

 nected with the motor threads spreading to the muscular fibres concerned, there is 

 no special effort necessary, beyond that which these cells would have exerted had 

 the movement been determined by horizontal internuncial threads arising from 

 cells acted on by afferent nervous threads from a cutaneous or mucous surface. 

 If there be anything entitled to the name of effort, it must be the same in a 

 simple reflex act as in a voluntary act. 



Hitherto but a part of the doctrine taught b}^ Whytt in the work under con- 

 sideration has been exhibited. He extended his principle to account for the ordi- 

 nary action of the heart, blood-vessels, the organs of secretion, and generally to 

 all the organs of the living body, concerned in what is called its vegetative life. 

 This department of the subject he worked out with much pains, and endeavoured 



