IN a study of the effects of ions on the rat diaphragm, it has been found that denervated preparations are much more sensitive to potassium than the normal diaphragm stimulated through its nerve. A dose of potassium, for example, exposure to a concentration of 0·08 per cent in Krebs's solution, which has no depressant action on normal muscle, may completely depress the response of denervated muscle to electrical stimuli while its response to acetylcholine remains. Observations have now been made on diaphragms denervated functionally by curare, which prevents the action of acetylcholine, or by lack of glucose, which prevents its synthesis or release. The effect is the same in both cases. If now, however, the experiment is reversed and the potassium added first, it is found that after curare, or through lack of glucose, which abolish neuromuscular transmission, the muscle has become inexcitable. The exact cause of this somewhat dramatic finding is not certain.