1. A considerable proportion of R. pipiens caught in the spring and stored without food for several weeks at about 4°C. had gastrocnemii that did not break down glycogen when they contracted anaerobically to complete exhaustion. A smaller number of the same muscles did not produce lactate.

2. There was no evident relation between failure to break down glycogen and the glycogen content of such muscles, some of which had more than 500 mg. of glycogen per 100 gm. of tissue.

3. The hypothesis of Meyerhof and his followers that aerobic contraction of frog muscles may at times take place with sources of energy other than carbohydrate is therefore extended to include anaerobic contraction.

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