The viscous elastic properties of smooth muscle

When the striated muscle of a frog is instantaneously released during an isometric tetanus its tension falls immediately by an amount depending on the extent of the release, to zero if the release be more than about 10 per cent. of its length; it then rises again along a curve similar to that of the initial rise of tension when stimulation began. This led Gasser and A. V. Hill (1) to deduce that the processes, whatever they be, which determine the development of a contraction when a tetanus begins, are the same as those which determine the redevelopment of the contraction after a sudden release during a tetanus. The observation and the deduction from it were used by Garner (2) in support of his hypothesis that contraction is due to the formation of some molecular pattern in the muscle substance, of something analogous to liquid crystals on the surfaces or throughout the volume of the fibre. It was obviously desirable to test this observation—of what is perhaps the simplest and most fundamental of the phenomena described by the term “viscous-elastic”—on some contractile tissue as different as possible from the voluntary muscle of the frog. During a recent visit to the Marine Biological Laboratory at Plymouth, Mr. C. F. A. Pantin and Mr. G. P. Wells introduced me to the longitudinal muscles of the body wall ofHolothuria nigra , a set of five smooth muscles running the whole length of the animal’s body, easy to prepare, able to survive for long periods in sea-water, and capable of being excited, either by single shocks or by a slow tetanus, to produce a very considerable tension.