350 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



may be produced by the reaction of the ganglionic centres to the impressions 

 made upon them. Such movements, however, being only called forth through 

 the intermediation of sensation, are distinguished as " sensori-motor" or " con- 

 sensual." Superadded to the mere sensorium, however, in Man and all the 

 higher animals, we find certain other ganglionic masses, the Cerebral hemispheres, 

 whose functional relation to the operations of mind is yet more intimate ; for 

 these appear to be the instruments of all the higher psychical operations, the 

 formation of ideas, the excitement of the emotions, the acts of combination, com- 

 parison, and judgment, the determinations of the will, &c. They receive their 

 first stimulus to action, not from impressions transmitted to them directly from 

 the peripheral organs, but from an agency sent up to them from the sensorial 

 centres; and it seems probably to be, in like manner, through an agency reflected 

 downwards to those centres, and acting through their instrumentality, that the 

 influence of the will, of emotional states, &c., is transmitted to the motor appa- 

 ratus. Thus we see that the nervous force, itself excited by impressions of a 

 physical nature, can determine mental changes ; whilst, conversely, certain states 

 of mind, by exciting the nervous force, can effect changes in the bodily fabric, 

 and, through this, upon the external objects within its reach. 



352. The instrumentality of the Nervous system is not limited, however, to 

 the excitation of mental activity on the one hand, or to that of muscular con- 

 traction on the other; for the peculiar agency which it exerts is found to have 

 an intimate relationship with all the other manifestations of vital force, which 

 the animal organism exhibits. So intimate, indeed, is this relationship so 

 obvious is the influence which nervous agency exerts over the operations of Nu- 

 trition, Secretion, &c., especially in the higher animals that many physiologists 

 have regarded them as essentially dependent upon it. For this assumption, 

 however, there is no valid evidence; and the whole tendency of recent discovery 

 has been (as we have seen) to establish the doctrine of the essential independence 

 of the vital endowments of each integral part of the fabric. And all the 

 phenomena which have been supposed to indicate the necessity for nervous 

 agency, as a condition of acts of growth, development, &c., are equally expli- 

 cable upon the doctrine here advocated, which affords a definite scientific ex- 

 pression of them. For, just as Electricity, developed by Chemical change, may 

 operate (by its correlation with chemical affinity) in producing other chemical 

 changes elsewhere so may Nerve-force, which has its origin in Cell-formation, 

 excite or modify the process of cell-formation in other parts, and thus influence 

 all the vital manifestations of the several tissues, whatever may be their own 

 individual characters. This expression is also available for the well-known in- 

 fluence of mental states upon the properties of the various tissues and the com- 

 position of the secretions; since this influence can only be exerted through the 

 instrumentality of the nervous apparatus. Further, it not only appears that a 

 simple withdrawal or disturbance of the nervous force supplied to particular 

 organs, occasions a retardation or perversion of their vital operations ; but there 

 also seems evidence that an influence of an opposite kind may be transmitted 

 through the nervous system, which is positively and directly antagonistic to the 

 exercise of the vital powers of the several tissues. Such, at least, appears to 

 be the only legitimate mode of accounting for the extraordinary effect of "a 

 shock," physical or mental, in at once and completely destroying the contrac- 

 tility of the heart, and in bringing to a stand the vital operations of other parts 

 ( 321). And it harmonizes well with the fact that, in Hemiplegia, the " palsy- 

 stroke" transmitted from the brain along the spinal cord, almost invariably affects 

 the leg less injuriously than the arm, and for a shorter duration; recovery tak- 

 ing place soonest in the leg, even when it has been at first paralyzed as com- 

 pletely as the arm. If the Nervous force be regarded as a polar force ( 364, 



