THE NERVOUS MECHANISM OF MICTURITION

It has frequently been stated that micturition is dependent on the integrity of a centre in the lumbo‐sacral region of the cord and on the connexions of this with the bladder and urethra, and that micturition takes place when this part of the cord is isolated from the parts of the central nervous system above it. Some authors even go so far as to state that a centre exists in the ganglia outside the cord, and that micturition can take place with these alone intact after removal of the lower end of the cord. As far as the cat is concerned this conclusion is proved to be false by the single experiment of dividing the sacral posterior (dorsal) roots, when micturition is permanently abolished. The escape of urine in jets and the reflex production of bladder contractions, after transection of the cord, are the two chief facts brought forward to support the hypothesis of a centre for micturition in the lumbo‐sacral cord, and whether or not the bladder empties itself has not been considered. The first, as has been explained, can occur without any co‐ordination. The second is what would be expected from the anatomical fact that the fibres of the pelvic nerve arise from cells situated in this part of the cord (2). The fact that in a normal cat a motor tone arising from above the lumbo‐sacral region is constantly passing out through the pelvic nerves, and a similar inhibitor tone through the hypogastrics, is quite inexplicable on the supposition of a lumbo‐sacral centre. That various factors in the function of micturition can and in some cases do arise in this part of the cord, and even, as has been shown, in the inferior mesenteric ganglia, is certain; but that any mechanism for piecing them together in a co‐ordinate act of micturition exists below the lower thoracic region of the cord is entirely without proof, whether one considers the various factors in the act or the ways in which the whole function is affected by thoracic transections of the cord. If the facts already stated are reviewed it will be seen that except for the inhibitor tone exercised on the bladder, which may quite probably prove to be something rather peculiar to the cat (2), the hypogastric appears to play little if any part in ordinary micturition. Even the closing mechanism of the bladder, which of all things one would expect to be due to a nervous motor tone, is seen to be independent of the hypogastrics. It would seem from this that the hypogastrics are only for use on certain occasions, as for instance, in coitus. A little support is lent to this suggestion by the fact that in guinea‐pigs during sexual excitement jets of urine are constantly shot out of the urethra; that the bladder is not emptied by this process is seen from the fact that the animals can continue doing it for a considerable time. Peripheral stimulation of the hypogastric in the guinea‐pig is followed by a very powerful contraction of the bladder.