MOVEMENTS OF THE ALIMENTARY CANAL, ETC. 327 



is required upon this point. The act of vomiting may be produced not only 

 as a reflex from various sensory nerves, but may also be caused by direct 

 action upon the medullary centres. The action of apomorphia is most easily 

 explained by supposing that it acts directly on the nerve-centres. 



Micturition. The urine is secreted continuously by the kidneys, is car- 

 ried to the bladder through the ureters, and is then at intervals finally ejected 

 from the bladder through the urethra by the act of micturition. 



Movements of the Ureters. The ureters possess a muscular coat consisting of 

 an internal longitudinal and external circular layer. The contractions of this 

 muscular coat are the means by which the urine is driven from the pelvis of the 

 kidney into the bladder. The movements of the ureter have been carefully 

 studied by Engelmann. 1 According to his description the musculature of the 

 ureter contracts spontaneously at intervals of ten to twenty seconds (rabbit), the 

 contraction beginning at the kidney and progressing toward the bladder in the 

 form of a peristaltic wave and with a velocity of about twenty to thirty milli- 

 meters per second. The result of this movement should be the forcing of the 

 urine into the bladder in a series of gentle rhythmic spirts, and this method of 

 filling the bladder has been observed in the human being. Suter and Mayer 2 

 report some observations upon a boy in whom there was ectopia of the bladder 

 with exposure of the orifices of the ureters. The flow into the bladder was 

 intermittent and was about equal upon the tw r o sides for the time the child 

 was under observation (three and a half days). 



The causation of the contractions of the ureter musculature is not easily 

 explained. Engelmann finds that artificial stimulation of the ureter or of a 

 piece of the ureter may start peristaltic contractions which move in both direc- 

 tions from the point stimulated. He was not able to find ganglion- cells in the 

 upper two-thirds of the ureter, and was led to believe, therefore, that the con- 

 traction originates in the muscular tissue independently of extrinsic or intrinsic 

 nerves, and that the contraction wave propagates itself directly from muscle- 

 cell to muscle-cell, the entire musculature behaving as though it were a single, 

 colossal hollow muscle-fibre. The liberation of the stimulus which inaugurates 

 the normal peristalsis of the ureter seems to be connected with the accumulation 

 of urine in its upper or kidney portion. It may be supposed that the urine 

 that collects at this point as it flows from the kidney stimulates the muscular 

 tissue to contraction, either by its pressure or in some other way, and thus leads 

 to an orderly sequence of contraction waves. It is possible, however, that the 

 muscle of the ureter, like that of the heart, is spontaneously contractile under 

 normal conditions, and does not depend upon the stimulation of the urine. 

 Thus, according to Engelmann, section of the ureter near the kidney does not 

 materially affect the nature of the contractions, of the stump attached to the 

 kidney, although in this case the pressure of the urine could scarcely act as a 

 stimulus. Moreover, in the case of the rat, in which the ureter is highly con- 

 tractile, the tube may be cut into several pieces and each piece will continue to 



1 Pfliiger's Archivfur diegesammte Physiologie, 1869, Bd. ii. S. 243; Bd. iv. S. 33. 



2 Archivfur exper. Pathologic und Pharmakologie, 1893, Bd. 32, S. 241. 



