Osmoregulation in the Muscle Fibres of Carcinus Maenas

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Abstract
1. Measurements have been made of the freezing-point depression of single muscle fibres of Carcinus maenas and of the concentrations of the non-protein nitrogenous components of the muscle. 2. When the blood is diluted the osmotic activity of the muscle fibres always falls in proportion. The fibres are probably always in osmotic equilibrium with the blood. 3. The osmotic activity of the fibres can be accounted for in terms of the concentrations of the muscle ions together with nitrogen-containing compounds, such as free amino acids, taurine and trimethylamine oxide. These organic substances account for over 60% of the total osmotic pressure. 4. In crabs from dilute sea water the concentrations of the nitrogenous compounds are reduced below the level expected from the increase in water content of the muscle. It is suggested that the muscle fibre can prevent excessive water intake by the removal of nitrogenous substances, thus reducing the internal osmotic activity. The process is reversible. 5. The importance of the mechanism in relation to the adaptability of the cell to reduced blood concentration is discussed.