330 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



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. 



Nervous 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 fibres 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 2 the spinal sensory fibres 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 contraction 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 

 centre. Langley and Anderson, 3 who also obtained this effect, give it a special 

 explanation, contending that it is not a true reflex. 



The immediate spinal centre through which the contractions of the bladder 

 may be reflexly stimulated or inhibited lies, according to the experiments of 

 Gfoltz, in the lumbar portion of the cord, probably between the second and fifth 

 lumbar spinal nerves. In dogs in which this portion of the cord was isolated 

 by a cross section at the junction of the thoracic and lumbar regions, micturi- 

 tion still ensued when the bladder was sufficiently full, and could be called 

 forth reflexly by sensory stimuli, especially by slight irritation of the anal 

 region. 



1 Journal of Physiology, 1895, vol. xix. p. 71. 



2 Pfliiger's Archivfiir die gesammte Physiologic, 1891, Bd. 49, S. 141. 



3 Journal of Physiology, 1894, vol. xvi. p. 410. 



