ACTION" AS A NERVOUS CENTRE. 469 



most energetic stimulus is derived from the spinal cord through the 

 sacral nerves. 



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

 is regulated by nervous influences coming from the cerebro-spinal sys- 

 tem alone. The contraction of the sphincter offers a resistance to the 

 escape of fluid from the bladder, which may be measured, and which 

 was found by Kupressow, 1 in the rabbit, to be equal to the pressure of 

 a column of water more than 40 centimetres in height. That is, if in 

 the living 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 centimetres 

 without any of it escaping by the urethra ; beyond that point the con- 

 tractile power of the sphincter was overcome, and the water was dis- 

 charged by the urethral orifice. 



The experiments of Kupressow also show that the nervous centre 

 upon which the sphincter vesicae depends for its reflex stimulus is in 

 the lumbar portion of the spinal cord. For if the cord were divided at 

 the level of the first or second lumbar vertebrae, no difference was per- 

 ceptible in the amount of resistance to pressure offered by the sphincter ; 

 and sections at the levels of the third and fourth lumbar vertebrae made 

 a difference of only two centimetres. But if the section of the cord were 

 made at the fifth lumbar vertebra, the resistance of the sphincter was at 

 once reduced to 14 centimetres; 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 vesicae, although it may be 

 aided by an act of volition, is directly dependent upon a nervous centre 

 situated, in the rabbit, about the "middle of the lumbar portion of the 

 spinal cord ; since this contraction persists after the cord has been 

 separated from the brain by a section at or above the fourth lumbar 

 vertebra, while it disappears if the section be made at or below the fifth 

 lumbar vertebra, thus either destroying the nervous centre itself or 

 cutting off its communication with the bladder. 



Both the retention of the urine in the bladder and its evacuation may 

 also be accomplished without the aid of any voluntary act. This is 

 shown by the experiments of Goltz, 2 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 parts of the body, could often retain their urine for a con- 

 siderable time, and also evacuate it by a regular and forcible contrac- 

 tion of the bladder. 



In man, when the sensibility of the mucous membrane of the bladder 

 or neighboring parts is increased by inflammation, the reflex impulse to 

 micturition is increased in intensity, producing an intolerance of urine. 

 Under these circumstances the urine is discharged by a reflex act as 



1 Archiv fur die gesammte Physiologic. Bonn, 1872, Band v. p. 291. 



2 Archiv fur die gesammte Physiologic. Bonn, 1874, Band viii. p. 474. 



