IN two previous publications (1, 2) experiments have been described which show that in the cat two of the reflexes which go to make up micturition do not arise in the cord but in the brain stem, at approximately the level of a plane through the posterior parts of the inferior colliculi dorsally and the middle of the pons ventrally. The two reflexes in question were the only two which produced a powerful and sustained bladder contraction, and, to their abolition, the abolition of micturition resulting from transection of the spinal cord is apparently due. The first of these reflexes is evoked by distension of the bladder and leads to contraction of the bladder: its afferent and efferent paths are both in the pelvic nerve. The second reflex is evoked by running fluid through the urethra and leads to contraction of the bladder; its efferent path is in the pelvic nerve and its afferent in the pudic and apparently also, or occasionally, in the hypogastric. Another reflex leading to contraction of the bladder was found, but this was feeble and transitory. It arises in the spinal cord: it is evoked by distension of the posterior urethra, both its afferent and efferent paths are in the hypogastric nerves. The experiments to be described were made with a view to localising the parts of the brain with which these two reflexes are connected, and to observing the effect on micturition of their destruction.The only method by which parts of the interior of the brain can be stimulated or destroyed with any degree of precision and without extensive injuries to other parts of the brain is by means of the stereotaxic instrument devised by CLARKE, and first used by himself and HORSLEY in investigations on the cerebellum (4). I am indebted to Dr R. H. Clarke, not only for the loan of his own instrument, but also for a very large amount of valuable advice and help in the earlier experiments. The instrument used was of the older pattern, in which the needle can only be inserted horizontally or vertically (4); it was used in 1 The expenses of this research were defrayed by grants from the Medical Research Council and from the
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.
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