The priority of the heat production in a muscle twitch.

When a muscle has been soaked in a moderately hypertonic solution its mechanical response to a shock is delayed, but its heat production is almost normal and starts considerably earlier than its shortening. After a more hypertonic solution the mechanical response is abolished, but a substantial part of the heat production remains. These effects are rapidly reversed by soaking in a normal isotonic solution. They strengthen the previous conclusion that chemical reactions triggered by a stimulus precede the mechanical response.