Some factors which are correlated with swimming capacity in guinea pigs

¹ Physiology Division, U.S. Army Chemical Warfare Laboratories, Army Chemical Center, Maryland

Guinea pigs were forced to swim to exhaustion under various experimental conditions. Electrocardiograms taken on some animals showed T waves with high amplitude and take-off. Ventricular fibrillation was never observed. The length of swim in guinea pigs varied inversely with the logarithm of the rate of change of rectal temperature. Liver glycogen was found to decrease markedly after forced swimming. Blood glucose values showed no clear pattern of change. Blood lactic acid values at termination were elevated by at least 50 mg/100 ml. Swimming time was found to vary inversely with the logarithm of the rate of change of blood lactic acid. Swimming time was decreased significantly if the animals were forced to bear a load. At 20° and 30°C bath temperature, the ST₅₀ (reduction of swimming time to 50% of control) was obtained with a load equal to about 2.5% of the body weight. If guinea pigs were forced to swim in groups rather than alone, about 70% showed a decrease of at least 50% in expected swimming time. It is suggested that small mammals should be forced to swim singly rather than in groups to obtain precise results.