KIDNEY AND SKIN AS EXCRETORY ORGANS. 857 



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 form 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 Engel- 

 mann.* According to his description, the musculature of the ureter 

 contracts spontaneously at intervals of ten to twenty seconds (rab- 

 bit), the contraction beginning at the kidney and progressing 

 toward the bladder in the form of a peristaltic wave and with a 

 velocity of about 20 to 30 mms. per second. The result of this 

 movement should be the forcing of the urine into the bladder in a 

 series of gentle, rhythmical spurts, and this method of filling the 

 bladder has been observed in the human being. Suter and Mayerj 

 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 

 two 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 con- 

 tractions which move in both directions 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 contraction orig- 

 inates 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-fiber. Efforts 

 to show a regulatory action upon these movements through the 

 central nervous system have so far given negative results. 



Movements of the Bladder. The bladder contains a muscular 

 coat of plain muscle tissue, which, according to the usual descrip- 

 tion, is arranged so as to make an external longitudinal coat and an 

 internal circular or oblique coat. A thin, longitudinal layer of 

 muscle tissue lying to the interior of the circular coat is also de- 

 scribed. The separation between the longitudinal and circular 

 layers is not so definite as in the case of the intestine; they seem, 

 in fact, to form a continuous layer, one passing gradually into the 

 other by a change in the direction of the fibers. At the opening of 

 the bladder into the urethra, the musculature in the submucosa is 



* "Pfliiger's Archiv f. die gesammte Physiologic," 2, 243, 1869, and 4, 33; 



also Lucas, "American Journal of Physiology," 17, 392, 1906. 



t "Archiv f. exper. Pathologic und Pharmakologie," 32, 241, 1893. 



