306 SPECIAL PHYSIOLOGY. 



stance of the heart, and over the muscular coat of the arterial vessels. 

 The sympathetic nervous system might be designated the nervous sys- 

 tem of the vascular apparatus ; its ultimate branches constitute the 

 so-called van-motor nerves. We shall immediately see evidence of 

 this control, and of the manner in which it appears to be exercised ; 

 and we shall find that, even in this, function, it is more or less assisted 

 by, and subordinated to, the cerebro-spinal system. 



We may consider the special functions of this system, in relation to 

 sensation, motion, nutrition, and secretion, and to the physiological 

 connections between it and the cerebro-spinal system. 



The sympathetic nerve, when the parts to which it is supplied, are 

 in a state of health, does not appear to be sensitive itself, nor to trans- 

 mit sensory impressions; for there is no feeling in the parts to which 

 these nerves are distributed, when they are in a condition of health. 

 In disease, however, cramps and other pains, sometimes of a most 

 acute and depressing character, are experienced in them ; the effects, 

 as one would say, of an exaltation of the common sensibility without 

 any tactile sense. In experimental irritation of the sympathetic, pain 

 is produced, the amount of which seems to vary under different cir- 

 cumstances. In all cases, the stimulus must be powerful enough for 

 the effects of the impression to be transmitted to the cerebro-spinal 

 system, and reach the centre of common sensation; for the substance 

 of the sympathetic is itself insensible, and the sensibility of parts sup- 

 plied by its branches only, must be due to its connection with the cere- 

 bro-spinal system. Whether the effects of such impressions, are con- 

 ducted by afferent fibres, running direct from the sympathetic nerves 

 to the cerebro-spinal nerves, or whether they are' first conducted to 

 the sympathetic ganglia, and thence indirectly, by fibres originating 

 in the gray matter of the sympathetic ganglia, is riot quite certain. 

 If the former be true, the reason why the parts supplied by the sym- 

 pathetic nerves, are insensible in health, must be, because the number 

 of afferent cerebro-spinal fibres in them is so few; if the latter view 

 be correct, the insensibility of these parts in health, must depend on 

 the interruption, or cutting off, of the sensory impressions at the gan- 

 glia. Again, the increased excitability, produced in disease, either 

 compensates for the paucity of the afferent fibres, or else causes the 

 effects of the sensory impressions to be transmitted, with greater force, 

 through the ganglia. 



In regard to the control of the sympathetic nerve over the motions 

 of the parts to which it is supplied, it is in the first place, important 

 to note, that this system is never the path of the voluntary motorial 

 stimulus,, the movements of all the parts being strictly involuntary, or 

 entirely beyond the control of the will. Thus the movements of the 

 intestines, in urging onwards their contents, are reflex, and excited 

 through the sympathetic nerves, by the mechanical stimulus of the food. 



That the sympathetic nervous system influences the movements of 

 the parts to which it is supplied, is proved by irritation of the nerve, 

 and by its division. Irritation of the sympathetic nerve distributed 

 to the iris, causes that membrane to contract in its width, so that the 

 pupil becomes dilated. 



