The normal act of micturition is dependent upon a well-sustained contraction of the smooth musculature of the wall of the bladder. With lesions of the nervous system below the mid-brain affecting micturition, this contraction is faulty. The experiments were performed upon cats, using as anæsthetics dial ciba, which acts uniformly throughout the experiment, or ether. After decerebration through the optic colliculi the bladder emptied completely on as little as one-fourteenth the volume of fluid required to produce reflex micturition in the intact, anæsthetized preparation. Under these conditions the pressure rose very rapidly and the contraction of the muscles was forceful. Transection of the brain-stem below the acoustic colliculi abolished this reflex and no contraction sufficient to empty the bladder occurred. The bladder then showed retention with overflow. The conclusion was reached that tone in the musculature of the bladder is controlled by similar mechanisms to those that control tone in the striated musculature. There is evidence that the control of this tonic mechanism is largely a function of the cerebral motor cortex and is effective at the level of the spinal cord. The tonic control is carried out from areas in the cephalic portion of the hind-brain. A study of bladder abnormalities in man serve to illustrate the experimental findings.