580 THE URINARY APPARATUS [CH. XXXVIII. 



Extirpation of loth kidneys is fatal ; the urea, etc., accumulate in 

 the blood, and the animal dies in a few days; urseinic convulsions 

 do not usually occur in such experiments. 



Ligature of loth renal arteries amounts to the same thing 

 as extirpation of the kidneys, and leads to the same result. If the 

 ligature is released the kidney after a time again sets to work, but the 

 urine secreted at first is albuminous, owing to the epithelium having 

 been impaired by being deprived for a time of its blood supply. 



The Passage of Urine into the Bladder. 



As each portion of urine is secreted it propels that which is 

 already in the uriniferous tubes onwards into the pelvis of the 

 kidney. Thence through the ureter the urine passes into the bladder, 

 into which its rate and mode of entrance has been watched in cases 

 of ectopia vesicce, i.e. of such fissures in the anterior and lower part of 

 the walls of the abdomen, and of the front wall of the bladder, as 

 expose to view its hinder wall together with the orifices of the ureters. 

 The urine does not enter the bladder at any regular rate, nor is there 

 a synchronism in its movement through the two ureters. During fast- 

 ing, two or three drops enter the* bladder every minute ; each drop a's 

 it enters first raises up the little papilla through which the ureter 

 opens, and then passes slowly through its orifice, which at once again 

 closes like a sphincter. Its flow is aided by the peristaltic 

 contractions of the ureters, and is increased in deep inspira- 

 tion, or by straining, and in active exercise, and in fifteen 

 or twenty minutes after a meal. The urine is prevented from 

 regurgitation into the ureters by the mode in which these pass 

 through the walls of the bladder, namely, by their lying for between 

 half and three-quarters of an inch between the muscular and mucous 

 coats before they turn rather abruptly forwards, and open through 

 the latter into the interior of the bladder. 



Micturition. 



The desire to void the urine arises from a sense of fullness of 

 the bladder, and the increase of pressure in this viscus, which results 

 from its distension, is probably the most important factor in the 

 causation of the reflex. Mosso states that in the dog's bladder a 

 pressure of 20 cms. of water sets the reflex in action. 



The afferent impulse so produced finds its way to the sacral 

 region of the cord chiefly through the second and third sacral nerves, 

 and stimulates the so-called vesical centre, which is situated in the 

 grey matter there ; the reflex takes place perfectly well in an animal 

 whose spinal cord has been cut across as low as the lower part of the 

 lumbar region. It has therefore been proved that the reflex centre 



