764 PHYSIOLOGY OF DIGESTION AND SECRETION. 



the physiological mechanism by which this series of muscular con- 

 tractions, and especially the contractions of the bladder itself, are 

 produced. According to the frequently quoted description given 

 by Goltz,* the series of events is as follows: The distention of the 

 bladder by the urine causes finally a stimulation of the sensory 

 fibers of the organ and produces a reflex contraction of the blad- 

 der musculature which squeezes some urine into the urethra. The 

 first drops, however, that enter the urethra stimulate the sensory 

 nerves there and give rise to a conscious desire to urinate. If no 

 obstacle is presented the bladder then empties itself, assisted per- 

 haps by the contractions of the abdominal muscles. The emptying 

 of the bladder may, however, be prevented, if desirable, by a volun- 

 tary contraction of the sphincter urethrae, which opposes the effect 

 of the contraction of the bladder. If the bladder is not too full 

 and the sphincter is kept in action for some time, the contractions 

 of the bladder may cease and the desire to micturate pass off. Ac- 

 cording to this view, the voluntary control of the process is limited 

 to the action of the external sphincter and the abdominal muscles; 

 the contraction of the bladder itself is purely an unconscious reflex 

 taking place through a lumbar center. 



The experiments of Goltz and others, upon dogs in which the 

 spinal cord was severed at the junction of the lumbar and the tho- 

 racic regions, indicate that micturition is essentially a reflex act, 

 with its center in the lumbar cord, although the same observer has 

 shown that in dogs whose spinal cord has been entirely destroyed, 

 except in the cervical and upper thoracic region, the bladder emp- 

 ties itself normally without the aid of external stimulation. Mosso 

 and Pellacanit have made experiments upon women in which a 

 catheter was introduced into the bladder and connected with a record- 

 ing apparatus to measure the volume of the bladder. Their ex- 

 periments indicate that the sensation of fullness and desire to 

 micturate come from sensory stimulation in the bladder itself 

 caused by the pressure of the urine. They point out that the 

 bladder is very sensitive to reflex stimulation; that every psychical 

 act and every sensory stimulus is apt to cause a contraction or in- 

 creased tone of the bladder. The bladder is therefore subject to 

 continual changes in size from reflex stimulation, and the pressure 

 within it will depend not simply on the quantity of urine, but on 

 the condition of tone of its muscles. At a certain pressure the 

 sensory nerves are stimulated and under normal conditions mictu- 

 rition ensues. We may understand, from this point of view, how it 

 happens that we have sometimes a strong desire to micturate when 

 the bladder contains but little urine, for example, under emotional 



* " Archiv f . die gesammte Physiologie, " 8, 478, 1874. 

 t" Archives italiennes de biologie, " 1, 1882. 



