INTRODUCTION

The pioneering studies of Kölliker (3) in 1849 were the first to tackle this difficult tissue. He recognised its cellular structure and observed its widespread occurrence in the vertebrate organism – in the intestinal canal, glands, liver, uterus, spleen, arteries, bladder, sense organs, etc. Here it is often present in the form of bands embedded in other tissue, and these bands may run in more than one direction; their dissection therefore often presents much difficulty. Then the small diameter of the cells, only 2–5/μ at the widest part, and the invisibility of most of their contents in the light microscope must be remembered.

Moreover, the variability in behaviour of smooth muscles from different organs makes generalisations uncertain. This variability is seen, for example, in responses to pharmacological reagents, which may be quite different from those familiar with striated muscles, and which differ from one kind of smooth muscle to another. Again, though some smooth muscles have a complicated system of innervation in close association with the cell, in others (e.g. intestinal muscle) transmission of excitation directly from cell to cell leads to automatic rhythmic tension production. The phasic contraction is always slow; thus McSwiney & Robson (1) gave values for gastric muscle at 37° of 0.77 sec for the latent period, 1.7–2.7 sec for the rising phase and 2.8 sec for half relaxation time.