[From the Proceedings of the American Association for the advancement of Science, Vol. XXXV. Buffalo Meeting, August, 1886.] Vaso-motor nerves of the limbs. By Dr. H. P. Bowditch, Harvard Medical School, Boston, Mass. [abstract.] In most of the recent experiments on the vaso-motor nerves of the limbs, the temperature of t-lie skin has been taken as the index of vaso-mo¬ tor activity. It is evident, however, that by this method transitory changes cannot be recorded and quantitative results cannot be obtained. In exper¬ iments made with the pletliysmographic method, to which these objections do not apply, it was found that either a constriction, or a constriction fol¬ lowed by a dilatation, or a dilatation of the vessels of the leg, may be pro¬ duced by an electric stimulation of the sciatic nerve. The character of the result depends largely upon the strength and rapidity of the induction shocks used as a stimulus. In the following table are given the results of 909 observations of the effect of stimulations of the sciatic nerve with induction shocks of varying intensity and rate. Bate of Stimulation. WEAK. MEDIUM. STRONG. No.ol Obs. Per cent No. Of Obs. Ter cent No. of Obs. Per cent - -+ + - + - -+* 4* 0-4 in 1" 5-16 in 1" 30-64 in 1" 108 69 62 9.3 31.9 48.4 57.4 60.9 50.0 33.3 7.2 1.6 218 153 40 7.8 28.8 50.0 69.7 58.8 50.0 22.5 12.4 0. 142 109 8 6.3 5.5 37.5 69.7 89.9 62.5 23.9 4.6 0. The figures in the columns headed —, — -f- and -f- show in what per cent of the total number of observations the effect of the stimulation of each rate and strength was respectively a constriction, a constriction followed by a dilatation and a dilatation. It will be observed: 1. That with each rate and intensity of stimulation the result, in at least one-lialf of the ob¬ servations, is a constriction followed by a dilatation; 2. That with an increasing rate of stimulation the proportion of cases giving a simple dila¬ tation diminishes while (except with strong stimulations) that of cases giving a simple constriction increases. With slow irritations it was found that dilatations are more readily pro¬ duced with feeble than with strong irritations. Experiments with animals whose nerves had been cut several days previously showed that degenera¬ tion of the nerve causes the loss of its constricting earlier than that of its dilating power. It thus appears that the sciatic nerve contains fibres which both con¬ tract and dilate the vessels ; but the former effect being more prompt than the latter, both in its appearance and disappearance, the two effects never neutralize each other. A fresh nerve with a strong and rapid stimulation are the best condi¬ tions for producing constriction. A degenerated nerve with a feeble and slow stimulation are the best conditions for producing dilatation. (270) Salem Press, December, 1886.