METABOLISM 249 



behind/' peristalsis, and gravity. To Engelmann we owe our knowledge 

 of the muscular movements of the ureter. He found that true peri- 

 staltic waves pass from the kidney to the bladder every half -minute on the 

 average at the rate of 2 or 3 cm. per second (the muscle thus resting 

 half or two-thirds of the time). Cases of non-closure of the bladder-walls 

 during development (ectopia) show that the urine spirts into the bladder 

 at about half-minute intervals. The activity (frequency and power) 

 of these movements is increased by additional resistance in the tube. 

 The musculature of the ureter is classed by the myogenists as "auto- 

 matic," as if dependent largely on food-supply rather than on immediate 

 and continuous nervous actuation. In this respect the ureter is like the 

 heart, intestine, etc., each ureter being practically one continuous muscle- 

 fiber. On the neurogenic theory, resident nerve-cells control all these 

 activities. 



The bladder serves the double function of a reservoir and an expelling 

 viscus. The adult male bladder holds normally about 600 c.c., but it 

 may contain well enough three times that quantity. This distention 

 cannot, however, be said to be quite normal, being more or less harmful. 

 The bladder might, but injuriously, accommodate, therefore, a whole 

 day's urine, but it is ordinarily emptied when containing 400 or even 

 300 c.c. It performs its expelling-f unction by means of the elastic and 

 muscular tissues of its walls, aided by abdominal pressure. The ureters 

 enter very obliquely under the mucosa, somewhat as in the kidney, so 

 that the greater the pressure within the viscus the less likely is the urine 

 to return up the ureters. The smooth muscular fibers of the bladder 

 are roughly arranged in three layers, which, however, are much intermixed. 

 A thickened portion of the musculature at the bladder's outlet constitutes 

 the sphincter, which is usually in tonic contraction. Nerves w r ith ganglia 

 in their course pass both to the mucosa and to the muscle-tissue. The 

 bladder is thus supplied with sensory, motor, and vasomotor functions. 



Micturition, the voidance of urine from the bladder, consists of a co- 

 ordinated series of muscular contractions of the bladder, the abdomen, 

 and the urethra. In children up to about the eighth month the process is 

 purely reflex, for voluntary inhibition of the efferent nervous impulses has 

 not then been acquired, probably because of the undeveloped state of 

 the neurones. In adults, on the other hand, voluntary inhibition may 

 be continued until the bladder's contractile mechanism has become 

 temporarily paralyzed by the pressure, which over-stretches it. The 

 normal retention of urine is the result of a functional balance between 

 this pressure and the tpnus of the retaining sphincter. Gradually the 

 musculature accommodates itself to the incoming urine, there being no 

 cavity in the bladder immediately after micturition. Nothing is felt 

 of this increasing pressure until 300 or 400 cm. of urine have collected; 

 then, unless the attention is fixed on some absorbing pursuit, the person 

 becomes aware of a desire to micturate, especially if by mechanical 

 joggling a drop of urine is pushed through the sphincter into the very 

 sensitive beginning of the urethra. If micturition be then inconvenient, 



