152 FUNCTIONS OF THE NERVOUS SYSTEM. 



by particular states of mind, or by conditions of the bodily system ; and the 

 "Connection just traced satisfactorily accounts for this, and is itself sufficiently 

 explained. The intestinal tube, then, from the stomach to the rectum, is not 

 dependent upon the Spinal Cord for its contractility, but is enabled to propel 

 its contents by its own inherent powers ; still we find that here, as in other 

 instances, the nervous centres exert a general control over even the organic 

 functions, doubtless for the purpose of harmonizing them with each other, and 

 with the conditions of the organs of animal life. 



202. On examining the outlets by which the excretions are voided, we find 

 that they are placed, like the entrances, under the guardianship of the Spinal 

 Cord; subject, however, to some control on the part of the Will. In the lowest 

 animals, the act of discharging excrementitious matter is probably as involuntary 

 as are the acts immediately concerned in the introduction of nutriment ; and is 

 performed as often as there is any thing to be got rid of. In the higher classes, 

 however, such discharges are much less frequent ; and reservoirs are provided 

 yi which the excrementitious matter may accumulate in the intervals. The 

 associated movements required to empty these, are completely involuntary in 

 their character ; and are excited by the quantity, or stimulating quality, of the 

 contents of the reservoir. But, had volition no control over them, great incon- 

 veniences would ensue ; hence sensation is excited by the same stimulus which 

 produces the movements ; in order that, by arousing the will, the otherwise 

 involuntary motions maybe restrained and directed. There can be little doubt, 

 from the experiments of Dr. M. Hall, as well as from other considerations, that 

 the associated movements, by which the contents of the rectum and bladder are 

 discharged, correspond much with those of Respiration, being in their own 

 nature involuntary, but capable of a certain degree of voluntary restraint and 

 assistance : whilst the discharge of the contents of the vesiculae seminales 

 would seem to be completely automatic ; thus corresponding with the act of 

 deglutition. On the other hand, the sphincters, which antagonize the expellent 

 action, are usually maintained in a state of moderate contraction, so as to afford 

 a constant check to the egress of the contents of the cavities; and this condition 

 has been fully proved by Dr. M. Hall to result from their connection with the 

 Spinal Cord, ceasing completely when this is interrupted. On the other hand, 

 the sphincter is certainly in part controlled by the will, and is made to act in 

 obedience to the warning given by sensation ; and this voluntary power is fre- 

 quently destroyed by injuries of the Brain, whilst the Spinal Cord remains 

 able to perform all its own functions, so that discharge of the urine and faeces 

 occurs. In their moderate action, the expulsors and the sphincters may be 

 regarded as balancing one another, so far as their reflex action is concerned, 

 the latter having rather the predominance, so as to restrain the operation of the 

 former. But when the quantity or quality of the contents of the cavity gives 

 an excessive stimulus to the former, their action predominates, unless the will 

 is put in force to strengthen the resistance of the sphincter ; this we are fre- 

 quently experiencing, sometimes to our great discomfort. On the other hand, 

 if the stimulus is deficient, the will must aid the expulsors, in order to overcome 

 that resistance which is due to the reflex contraction of the sphincters ; of this 

 also we may convince ourselves, when a sense of propriety, or a prospective 

 regard to convenience, occasions us to evacuate the contents of the rectum or 

 bladder without a natural call to do so. The muscular coat of the Bladder is 

 commonly regarded as having, like that of the intestinal tube, no connection 

 with the Spinal Cord ; but the experiments of Valentin have shown that a con- 

 nection exists, as in the former case, through the sympathetic nerve, affecting 

 not only the bladder but also the ureters. That physiologist states, that a very 

 distinct and powerful peristaltic action of the ureter, proceeding from the 

 kidneys to the bladder, may be produced, by irritating the abdominal ganglia 



