The efflux of magnesium from single crustacean muscle fibres

1. In the large single muscle fibres from the barnacle Balanus nubilus, the total fibre Mg concentration was estimated as 15·1 m‐mole/kg wet wt., of which about 3–3·5 m‐mole/kg wet wt. was extracellular. The diffusible Mg, measured by internal sampling, was 11·5 m‐mole/kg wet wt., of which at least half may be complexed to larger diffusible molecules. The free ionized Mg level was estimated as < 5 m‐mole/kg wet wt.