THE SPINAL CORD. 411 



traction of the urinary bladder ; but these contractions are no longer 

 produced after dividing the roots of the sacral nerves. Irritation of 

 either the sympathetic or the spinal nerve filaments going to the hypo- 

 gastric plexus produces contraction of the bladder, more energetic in 

 the latter case than in the former. 



Disease or injury of the spinal cord causing complete paraplegia, is 

 usually accompanied by paralysis of the urinary bladder. The muscu- 

 lar contraction of the bladder is therefore under the influence both of 

 the sympathetic and cerebro-spinal systems; but its most energetic 

 stimulus comes from the spinal cord through the sacral nerves. 



The closure or relaxation of the sphincter vesicae, on the other hand, 

 is regulated by influences from the cerebro-spinal system alone. The 

 resistance of the sphincter to the escape of fluid from the bladder, 

 measured by Kupressow,* in the rabbit, was found equal to the press- 

 ure of a column of water more than 40 centimetres in height. That 

 is, if in this animal one of the ureters were closed by a ligature, and 

 an upright tube fastened in the other, the bladder and the upright 

 tube might be filled with water to a height, on the average, of 44 cen- 

 timetres without its escaping by the urethra ; beyond that point the 

 resistance of the sphincter was overcome, the water being discharged 

 by the urethral orifice. 



The experiments of Kupressow also show that the nervous centre 

 of reflex action for the sphincter vesicae is in the lumbar portion of the 

 spinal cord. If the cord were divided at the level of the first or sec- 

 ond lumbar vertebra, no difference was perceptible in the resistance of 

 the sphincter ; and sections at the third and fourth lumbar vertebrae 

 diminished it by only two centimetres. But if the cord were divided 

 at the fifth lumbar vertebra, the resistance was reduced to 14 centi- 

 metres ; and the same effect was produced by section at the sixth and 

 seventh vertebrae of the same region. The tonic contraction, therefore, 

 of the sphincter vesicoa, although it may be aided by volition, is directly 

 dependent on a nervous centre situated, in the rabbit, about the middle 

 of the lumbar portion of the spinal cord ; since it persists after the cord 

 has been separated from the brain by a section at or above the fourth 

 lumbar vertebra, but disappears after a section at or below the fifth 

 lumbar vertebra, thus destroying the nervous centre or cutting off its 

 communication with the bladder. 



Both the retention of urine and its evacuation may be accomplished 

 without the aid of volition. This is shown by the experiments of 

 Goltz,f who found that after division of the spinal cord, in dogs, 

 between the dorsal and lumbar regions, the animals, though deprived 

 of sensibility and voluntary motion in the posterior limbs, could often 

 retain their urine for a considerable time, and also evacuate it by a 

 regular and forcible contraction of the bladder. 



* Archiv fiir die gesammte Physiologie. Bonn, 1872, Band v., p. 291. 

 f Archiv fiir die gesammte Physiologie. Bonn, 1874, Band viii., p. 474. 



