Viscoelasticity of dog spinal cord

Longitudinal viscoelastic behavior of dog spinal cord was investigated by means of the stress-relaxation curve for various conditions. A 40-mm formalin-fixed piece showed little relaxation or relatively high elasticity. A freshly removed piece of cord displayed slightly longer relaxation at 5-20 degrees C than at 39-50 degrees C. The stress-relaxation curve for a 20-g load could be replicated several times with return to original length (viscous behavior). A 20-g load repeatedly applied before relaxation was complete or a 60-g load rapidly applied caused the 40-mm piece to elongate to twice its original length with no return to that length (plastic flow). The viscous coefficient was calculated for an average 20-g load at 39 degrees C from eta = epsilon tau = 3.54 x 10(7) poise. Histological examination of the tissue after rupture suggested that much of the viscoelasticity was due to glycosaminoglycans rather than axons.