SUMMARY

A method was described for the in vitro preservation of adult frog muscle tissues at 2 5 O ~ for up to 8 days, as judged by the criteria of resting potential, the K+ and ~ a + contents, and mechanical contractility. Since the earliest days of biology, frog muscle has been a highly useful experimental material. Yet this muscle and many other types of isolated tissues cannot usually last for experimental purposes for more than a few hours at room temperature. While this length of time is sufficient for kinetic and other short-term experiments, there are experiments which require a longer period of observation. The steady level of K', for example, is not reached until after seventy-two hours.''2 Cooling prolongs the survival time; it also corre-spondingly slows down the time to reach a new equilibrium. A method for the long-tern~ preservation of isolated frog muscle in an artificial medium beyond 72 hours, aside from meeting this particular need for longer-term experiments, also opens the way toward future studies on the long-lasting effects of hormones and drugs on mature, normal cells in a controllable manner. This paper reports the successful development of such a method for the preservation of isolated frog muscle at 25°C for at least 8 days. MATERIALS AND METHODS I. Materials All the experiments under consideration here were performed on the sartorius muscles of leopard frogs (Rana pipiens, Schreber), which were force-fed hamburger meat every 3 or 4 days in an aquarium provided with running water maintained at room temperature the year round