The Distribution and Exchange of Inorganic Ions in the Central Nervous System of the Stick Insect Carausius Morosus

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Abstract
1. The distribution and exchange of inorganic ions between the central and the haemolymph has been studied in the stick insect, Carausius morosus, by flame photometry and radioactive tracers. 2. The exchanges of labelled ions show rapid and slow components which correspond to extracellular and intracellular compartments within the central nervous system. 3. The uptake of sodium from the haemolymph and its concentration in the extra-cellular fluid is reduced in the presence of metabolic inhibitors. 4. The distribution between haemolymph and extracellular fluid of calcium and magnesium, and also of sodium in poisoned preparations, conforms to a Donnan equilibrium. The distribution of potassium, even in poisoned preparations, does not conform and it is suggested that the activity of this ion may be lower than in free solution. 5. The concentration of magnesium is appreciably greater in the extracellular than in the intracellular compartment. The possible role of magnesium in nervous transmission in this insect is discussed.