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