476 PHYSIOLOGY CHAP. 



during sleep is more concentrated than that of waking (Posner) 

 seems to indicate that the bladder does absorb some of the water 

 of the urine and concentrates it. But according to Kaupp, who 

 examined the composition of the urine in the bladder at different 

 times with a constant diet, no absorption of water takes place, but 

 only of urea, with excretion of sodium chloride. According to 

 Wundt, the concentration which the urine undergoes in the 

 bladder is greatest when the loss from the skin in the form of 

 sweat is also maximal. 



Gerota (1897) showed by his accurate work on absorption in 

 the bladder that the mucous membrane of the bladder, unlike 

 that of the urethra, contains no lymphatics, which, on the contrary, 

 are plentiful in the muscular coat, and probably communicate 

 with the lymph sinuses of the rnucosa. On injecting various 

 substances by puncture into the bladder, he arrived at the follow- 

 ing results : 



(a) The permeability of the mucous membrane of the bladder 

 is low owing to the multiple layers of the epithelium. 



(&) Substances which have large molecules, such as the 

 alkaloids, do not diffuse : those with small molecules diffuse, but 

 very slowly and in very concentrated solutions. 



(c) The diffusion of urea is too small to have any practical 

 importance. 



The later work of 0. Cohnheim (1901), who, after tying the 

 ureters, introduced into the bladder different solutions, the con- 

 centration of which was determined before and after the experi- 

 ment, shows, in accordance with the previous conclusions of 

 Lusini, Boyer and Guinard, Pousson and Ligalas, that the normal 

 bladder has no capacity of absorption. The walls of the bladder 

 are impermeable both to salts and pigments and to water. The 

 fluids introduced are preserved as unaltered as if they were in a 

 glass vessel. It is only when the walls are necrosed or profoundly 

 injured by the action of caustic or toxic substances (e.g. sodium 

 fluoride) that they become permeable and assume the character of 

 an ordinary diffusion membrane. 



Similar work, but with somewhat different results, was under- 

 taken by Galeotti and Fasola (1903). After previous ligation of 

 the ureters, they injected various solutions of sodium chloride or 

 saccharose into the bladder, which were hypo-, iso-, or hypertonic 

 to the blood, and of which the quantity and concentration were 

 exactly determined before and after the experiment. They made 

 two sets of experiments, one series being on the normal bladder, 

 the other on the bladder of which the walls were altered by 

 chloroform. The following were their results : 



(a) The epithelium of the bladder injured by chloroform 

 behaves like a ^semi-permeable membrane, through which osmotic 

 equilibrium is immediately established, with increase of volume if 



