A visco-elastic theory of mechanoreceptor adaptation.

1. Physical analysis of two visco-elastic models was performed, to afford a quantitative basis for examination of a theory of slip as applied to mechanoreceptor adaptation. In one model the coupling force between skin tissue and receptor was considered to be purely viscous; in another it was supposed to consist of parallel viscous and elastic forces, representing the properties of a gel.2. Predictions from the models were compared with experimental results from frog and rat skin receptors. Good fits with slope-latency and slope-amplitude curves were obtained, with the adjustment of two constants.3. The excitability changes during long subliminal stimuli showed dynamic and static phases, which developed at different rates as stimulus strength was increased. This behaviour could be explained qualitatively by the more complex model, but quantitative comparisons could not be achieved.4. Treatment of the skin with tissue-destroying enzymes caused changes in stimulus-response relationships consistent with predictions from the models. The effect of the enzymes seemed to be largely on the elastic coupling forces.5. The visco-elastic model offers a satisfactory but not exclusive explanation of certain time- and amplitude-dependent features of mechanoreceptor behaviour and also accounts for a specific delay in mechanical excitation.