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trickle past. After removal of the stylet a conical adapteris fitted to the cannula and connected via a piece of rubbertubing to a glass tube that reads the pressure. The glasstube is then lowered, the required amount of fluid iscollected, the cannula is removed and the site of thepuncture covered with cotton and iodoform collodion. Ifblood or fluid at first continue to escape brief pressuresuffices to stop the leak. The patient must rest in bedfor 24 hours following the puncture.The level of the liquid in the glass tube indicates themean cerebrospinal fluid pressure at the corresponding levelin the subarachnoid space. Respiratory and often alsopulsatile fluctuations of up to 1 mm are visible in thelevel, although their amplitude and timing are modified bythe narrow bore of the cannula. The fluid level may alsoshow slower changes in level of 10 to 20 mm (over one ormore minutes), caused by change of position, musculartension, or perhaps even vascular innervation. Immobilityof the fluid level signifies that the opening of the cannulais obstructed by a nerve root or by connective tissue;patency can usually be restored by a slight twist of theneedle or a change in posture.If one allows fluid to drain the pressure will fallcorrespondingly and will usually show a tendency to recoverwhen the outflow ceases.To achieve a more prolonged pressure pressure relief ofthe subarachnoid space I used a needle whose orifice hadbeen enlarged to a lanceolate shape about 2 mm long andattempted to create a slit in the dura on withdrawal (case2, punctures 3,4,5), That continued leakage of fluid didoccur was evidenced by the slight edema that developedaround the site of the puncture. A more effective way ofattaining this result was achieved with punctures 5 and 6when I introduced a slender lancet (4 mm wide) through thedura in the midline: after 8 days the pressure in thesubarachnoid space was still several centimeters lower thanpreviouly, and after the second lancet stab the edema of thesurrounding tissues clearly testified to the continuingescape of cerebrospinal fluid. Case No. 5 indicated, to besure, that such an opening can become obstructed byarachnoid membrane or by clot.