The cerebrospinal fluid.

Sinclair and Hinshaw (1951) reported that ischaemic tingling was diminished or absent in patients with spinal or cerebral lesions causing defective tactile sensibility, and suggested that " It may even be that a diminution in the sensation of tingling affords a more sensitive test for such defects than standard testing methods ". However, the present work suggests that the relation between tingling and tactile loss is not a simple one. In the group of spinal cord lesions, ischaemic tingling was short-lived or absent in all the patients with a raised tactile threshold and a reduced " time to numbness " (Cases 2, 3, and 4), and in Case 5 ischaemic tingling returned as sensation improved after operation. In those with cerebral lesions, however, ischaemic tingling was absent in only one case (Case 6), and reduced or delayed in two (Cases 8 and 9). In Cases 7 and 11 ischaemic tingling was present although there was considerable sensory loss and a reduced " time to numbness " in each case. Marshall (1952) found that in patients with sciatica due to lumbar disc degeneration, ischaemic tingling sometimes occurred earlier in the affected foot than in the normal one. Marshall explained his results by suggesting that there were degenerative changes in the distal segments of the affected nerve fibres which rendered them more irritable during ischaemia. His results could, however, be explained by the simple additive effect of two separate irritative foci along the course of the nerve, one at the level of the lesion and the other under the pneumatic cuff. If, in patients with spinal and cerebral lesions, irritable foci at different levels can exert an additive effect, the intensity of ischaemic paraesthesiae would presumably depend upon the response of ischaemic nerve peripherally and upon the amount of irritation and spontaneous discharge occurring in the central lesion. The latter would not necessarily be related to the severity of the lesion in terms of other sensory defects. SUMMARY In 11 patients with sensory loss in the hand due to spinal or cerebral lesions, the circulation to the affected arm has been arrested by a pneumatic tourniquet. When a partial peripheral nerve block has been produced in this way, its effect on sensation has been added to that of the central lesion and has resulted in sensory loss in excess of that produced by either one alone. In patients with spinal cord lesions, …