DYNAMICS OF HISTOGENESIS 349 



recorded through the inlet tube. The down-stroke represents 

 vesicular contraction simultaneous with urethral relaxation cor- 

 responding to the time that the bladder is being emptied and the 

 concomitant reduction of back pressure through the inlet tube. 

 These curves were made with the mechanical valve working be- 

 tween the elevated pressure reservoir and the mercury manometer. 

 They are of different types : some are single, others double hillocks, 

 while some show the pressure rising gradually and then a sudden 

 release with the contraction of the bladder. Certain curves show 

 a comparatively acute summit, others a definite plateau. This 

 indicates a variable irritability and response of the modified 

 vesicular musculature to the constant extrinsic tensile stimulus. 



The contractions of the bladder musculature are active and inde- 

 pendent of the action of the heart and respiration (table 2) . With 

 each bladder contraction determined by the manometer and by 

 palpation there is an expulsion of urine. This expulsion is due to 

 vesicular contraction and not to a passive transmission through the 

 bladder on account of any active zone extrinsic to the contracting 

 vesicle. The abdominal musculature is in a state of normal 

 tonicity and shows absolutely no simultaneous activity with the 

 relaxation of the urethra, bladder contraction, and fluid expulsion. 

 The dog slept practically throughout the tinije that the record 

 labeled figure 14 was being made. 



With overdistention of the bladder the dog experienced forced 

 respiratory movements. These, naturally, had their immediate 

 effect on the vesicular pressure, just as they do normally. The 

 optimum bladder rhythm was an independent series of contrac- 

 tions, which was not caused by any indirect influence from the 

 respiratory or cardiac regions. The elongated respiratory waves 

 upon which the cardiac rhythm is superimposed in normal pulse 

 tracings are obtained as seen in figure 20. 



THE TRANSFORMATION OF THE BLADDER MUSCULATURE 



Gross observations. At the initial operation the bladder pre- 

 sented the appearance of smooth muscel on inspection. Very 

 little resistance was met on cutting through the bladder wall, which 

 measured 0.5 mm. in thickness. At the second operation the 



