THE EFFECT OF INITIAL TENSION AND LOAD ON THE RESPONSE OF THE NICTITATING MEMBRANE OF THE CAT

Abstract

The average optimum initial tension for 18 observations on 13 nictitating membranes was 10.75 [plus or minus] 0.37 gm. The tension increment-initial tension relations are the same whether excitation is effected through intravenously injected adrenalin or through stimulation of the cervical sympathetic nerve. Tension-length curves for relaxed and contracted states of the nictitating membrane during stretching and releasing stages are presented. The tension increment-length curves during stretching and re- leasing stages are practically identical. The influence of load on the isotonic response of the smooth muscle of the nictitating membrane has been determined, and the effect of increasing load on the external work is graphically presented. The average optimum load for 7 different preparations was found to be 11.57 [plus or minus] 0.88 gm. The maximum response of the nictitating membrane in isometric contraction is reached only after extension has been carried beyond the greatest physiological length.