322 INNERVATION. [CHAP. XI. 



of this question, the two following propositions: 1. That the 

 brain, or some part of it, is the sensorium commune; or, in other 

 words, that mental nervous actions (acts of volition and sensation) 

 cannot take place without the brain. 2. That the vesicular is the 

 truly dynamic nervous matter, the source of all nervous power.* 



The following hypothesis have been proposed in explanation of 

 these actions. 



1 . The various muscles and sentient surfaces of the body are 

 connected with the brain by nerve-fibres, which pass from the one 

 to the other. Those fibres destined for, or proceeding from, the 

 trunk to the brain, pass along the spinal cord, so that that organ is 

 in great part no more than a bundle of nerve-fibres going to and 

 from the brain. These fibres are specially for sensation and volun- 

 tary motion. 



But, in addition to these, there is another class of fibres proper to 

 the spinal cord and to its intra-cranial continuation, which form a 

 connexion with the gray matter of the cord. Of these fibres, some 

 are afferent or incident, others efferent or reflex, and these two 

 kinds have an immediate but unknown relation to each other, so 



* The first of these postulates will be considered farther on in this chapter. 

 The second appears to us to have a sufficiently firm foundation to warrrant us 

 in assuming its correctness, for the sake of arguing the important question re- 

 ferred to in the text. We shall state briefly here the proofs that the associa- 

 tion of the vesicular and fibrous matter is necessary to the development of 

 nervous force. 



1. Nerves, when separated for a time from the nervous centre, lose all power 

 of stimulating their muscles to contraction. No irritation, mechanical or elec- 

 trical, is sufficient to excite them. If a nerve be divided some distance from 

 the centre, the peripheral portion will, after a time, waste, and lose all power of 

 developing nervous force ; but the central portion, which remains in connexion 

 with the centre, retains its nutrition and its vital properties unimpaired. 



2. All nervous centres contain vesicular matter, with which nervous fibre 

 freely intermix. 



3. The power of a nervous centre appears to be proportionate to the quantity 

 of its vesicular matter. This is well exemplified in the cerebral convolutions, 

 the vesicular surface of which is always in the direct proportion of the de- 

 velopment of mental power ; or, in general terms, the gray matter increases in 

 the exact ratio of the nervous energy. (Grainger). 



4. All nerves appear to rise from vesicular matter. Stilling represents 

 special accumulations of vesicular matter at the origins of the nerves of the 

 medulla oblongata. 



5. Nerves, whose power is exalted for some special purpose, have an increased 

 quantity of gray matter at their origin, of which the electric lobe in the torpedo, 

 connected with the origins of the fifth and eighth pairs of nerves, is an extraor- 

 dinary instance. See Mr. Grainger's excellent work on the spinal cord, pp. 18-21- 



