. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 148 A. SZENT-GYORGYI In the rabbit, experiments were performed in a similar way with the smaller weight (Fig. 5). Experiments were performed with strips of the musculus gracilis similar in dimensions to the frog sartorius. These strips were cut parallel to the fibres. The experiment was performed soon after the animal's death. The results were similar to those obtained in the frog. In both cases the muscle went into permanent maximal contraction at the temperature where the A F curve cuts the 11,000 calorie level, as demande
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 148 A. SZENT-GYORGYI In the rabbit, experiments were performed in a similar way with the smaller weight (Fig. 5). Experiments were performed with strips of the musculus gracilis similar in dimensions to the frog sartorius. These strips were cut parallel to the fibres. The experiment was performed soon after the animal's death. The results were similar to those obtained in the frog. In both cases the muscle went into permanent maximal contraction at the temperature where the A F curve cuts the 11,000 calorie level, as demanded by the theory. The fact that maximum and permanent contracture was reached only where the expenditure of F was 11,000 shows that the transference of energy from ATP to the contractile system goes without considerable loss. This heat contracture must not be confused with the shortening of muscle due to heat denaturation. If a muscle is immersed into Ringer of 70° C. an extensive shortening is pro- duced which is not due to the mobilization of the normal mechanism of contraction, but to denaturation. The difference between the two processes can easily be demonstrated. If the muscle is stored a few hours after death at room temperature or overnight in the ice box, the ATP disappears. No rapid contraction will be obtained at 53° in this muscle, but shortening will still be obtained at higher temperatures at which rapid denaturation is produced. This denaturation manifests itself, also, by a turbid appearance. The basic difference between the contraction obtained in the presence of ATP at 53° in the rabbit or 47° in the frog, due to the mobilization of the normal mechanism of contraction, and the shortening produced at higher temperatures and due to denaturation, can be demonstrated, also, by connecting the muscle to I2OOO 10000 8OOO 6000 4000 2000 UOOO 5500 O o O. A * C° 0 10 20 30 40 50 FIGURE 6. The work performed by strips of rabbit psoas, after freezing and thawing, at v
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
