436 



ABSORPTION. 



The afferent or sensory fibres are also connected with the brain. The automatic centre maintains 

 the closure of the bladder, but if the latter be distended, different impulses proceeding from it 

 reach the spinal centre, and it may be the cerebrum. The impulses reaching the automatic 

 centre inhibit its action and those to the reflex centre excite it, so that the detrusor urine con- 

 tracts. If the afferent impulses be powerful, a desire to urinate is excited, and voluntary 

 impulses are excited which act upon the spinal centres as the 

 afferent impulses do, and thus the act of urination is more easily 

 accomplished.] 



We may conceive a voluntary impulse to pass down special 

 fibres to an inhibitory centre, which may either act directly on 

 the motor centre, or possibly may send branches directly to the 

 sphincter muscles. 



Painful stimulation of sensory nerves causes reflex contraction 

 of the bladder and evacuation of the urine (in children during 

 teething). Reflex contraction of the bladder can be brought about 

 in cats, by stimulation of the inferior mesenteric ganglion. After 

 section of all the nerves going to the bladder, haemorrhage and 

 asphyxia cause contraction by a direct effect upon the structures 

 in the wall of the bladder. As yet no one has succeeded in excit- 

 ing artificially the inhibitory centre in the brain for the sphincter 

 muscle (Sokoivin and Kowalcsky). 



It seems probable that, as in the case of the anal sphincter 

 ( 160), there is not a continuous tonic reflex stimulation of the 

 sphincter urethra ; the reflex is excited each time by the contents. 

 The sphincter vesicae of the anatomists, which consists of smooth 

 muscular tissue, does not seem to take part in closing the bladder. 

 Budge and Landois found that, after removal of the transversely 

 striped sphincter urethra, stimulation of the smooth sphincter 

 did not cause occlusion of the bladder, nor could L. Rosenthal 

 or v. Wittich convince themselves of the presence of tonus 

 in this muscle. Indeed, its very existence is questioned by 

 Henle. 



Changes of the Urine in the Bladder. When the urine is 



retained in the bladder for a considerable time, according to 



and cerebral centres ;B.,blad- Kaupp, there is an increase in the sodium chloride and a decrease 



der; S., sensory centre acted i n the urea and water. Urine which remains for a long time in 



on by afferent impulses. the bladder is prone to undergo ammoniacal decomposition. 



Absorption. Many observers have shown that the mucous membrane of the bladder is 



capable of absorbing substances potassium iodide and other soluble salts. [Ashdown has shown 



that poisons, such as watery solutions of strychnin, curare, eserin, emulsions of chloroform and 



ether, are absorbed when injected into the bladder of rabbits. In rabbits, KI injected into the 



bladder through a catheter was found in the urine obtained from the divided ureters. Water 



and urea are also absorbed the latter in larger proportion than the former.] 



As the ureters enter near the base of the bladder, the last secreted urine is always lowest. If 

 a person remain perfectly quiet, strata of urine are thus formed, and the urine may be voided so 

 as to prove this (Edlefscn). 



The pressure within the bladder, when in the supine position = 13 to 15 centimetres of 

 water. Increase of the intra-abdominal pressure (by inspiration, forced expiration, coughing, 

 bearing-down) increases the pressure within the bladder. The erect posture also increases it, 

 owing to the pressure of the viscera from above {Schatz, Dubois). [James obtained 4 to 4*5 inches 

 Hg as the highest expulsive power of the bladder including the abdominal pressure, voluntary 

 and involuntary. In paraplegia, where there is merely, the expulsive power of the bladder, he 

 found 20 to 30 inches of water.] 



[Hydronephrosis occurs when the ureters and pelvis of the kidney become dilated, owing to 

 partial and gradual obstruction of the outflow of urine from the ureters : if the obstruction 

 become complete, there is cessation of the urinary secretion. James has shown that the bladder 

 remains contracted for several seconds after it is emptied, and this is specially the case in 

 irritable bladder; so that this condition may also give rise to hydronephrosis by damming up 

 the urine in the ureters.] 



Rapidity of Micturition. The amount of urine voided at first is small, but it increases with 

 the time, and towards the end of the act it again diminishes. In men, the last drops of urine, 

 are ejected from the urethra by voluntary contractions of the bulbo-cavernosus muscle. Adult 

 dogs increase the stream rhythmically by the action of this muscle. 



281 DETENTION AND INCONTINENCE OF URINE. Retention of urine or ischuria 



occurs : 1. When there is obstruction of the urethra, from foreign bodies, concretions, 

 stricture, swelling of the prostate. 2. Paralysis or exhaustion of the musculature of the 



Fig. 292. 

 Scheme of mictnrition : A.C., 

 R.C., C, automatic, reflex, 



