392 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



show thai the bladder may be emptied by a direci voluntary act. Tn these 

 experiments a catheter was introduced into the bladder and connected with 



a r< rding apparatus to measure the volume of the bladder. It was found 



that, in some cases at least, the woman could empty the bladder at will 

 without using the abdominal muscles. The same authors adduce experi- 

 mental evidence to show that the sensation of fulness and desire to mic- 

 turate come from sensory stimulation in the bladder itself caused by the 

 pressure of the urine. They point out that the Madder is very sensitive to 

 reflex stimulation ; that every psychical act and every sensory stimulus is 

 apt to cause a contraction or increased tone of the bladder. The Madder is, 

 therefore. subject t<> eoiitiiiual changes in size from reflex stimulation, and 

 the pressure within it will depend not simply on the quantity of urine, but 

 ■ m the condition of tone of the bladder. At a certain pressure the sen- 

 sorv nerves are stimulated and under normal conditions micturition ensues. 

 We may understand, from this point of view, how it happens that we have 

 sometimes a strong desire to micturate when the bladder contains bui little 

 urine — for example, under emotional excitement. In such cases if the micturi- 

 tion is prevented, probably by the action of the external sphincter, the bladder 

 may subsequently relax and the sensation of fulness and desire to micturate 

 pass away until the urine accumulates in sufficient quantity or the pressure is 

 again raised by some circumstance which causes a reflex contraction of the 

 bladder. 



\< rvous Mechanism. — According to a recent paper by Langley and Anderson, 1 

 the bladder in cats, dogs, and rabbits receives motor fibres from two sources: (1) 

 From the lumbar nerves, the fibres passing out in the second to the fifth lumbar 

 nerves and reaching the bladder through the sympathetic chain and the infe- 

 rior mesenteric ganglion and hypogastric nerves. Stimulation of these nerves 

 causes comparatively feeble contraction of the bladder. (2) From the sacral 

 spinal nerves, the fibre- originating in the second and third sacral spinal nerves, 

 or in the rabbit in the third and fourth, and being contained in the so-called 

 nervus erigens. Stimulation of these nerves, or some of them, causes strong 

 contractions of the bladder, sufficient to empty its contents. Little evidence 

 was obtained of the presence of vaso-motor fibres. According to Nawrocki 

 and Skabitschewsky a the spinal sensory fibre- to the bladder are found in part 

 in the posterior roots of the first, second, third, and fourth sacral spinal nerves, 

 particularly the second and third. When these fibres are stimulated they excite 

 reflexly the motor fibres to the bladder found in the anterior roots of the second 

 and third sacral spinal nerves. Some sensory fibres to the bladder pass by way 

 of the hypogastric nerves. When these are stimulated they produce, according 

 to these authors, a reflex effect upon the motor fibres in the other hypogastric 



nerve, causing a < traction of the bladder, the reflex occurring through the 



inferior mesenteric ganglion. This observation has been confirmed by several 

 authorities, and is the best example of a peripheral ganglion serving as a reflex 



'- Journal of Phyxiolgy, 1895, vol. xix. p. 71. 



- Archivfur <H> gesamnUe Physiologic, 1891, Bd. 49, S. 141. 



