The load-strain and stress-relaxation behavior of wet rat tail tendon has been examined with respect to the parameters strain, rate of straining, and temperature. It is found that this mechanical behavior is reproducible after resting tile tendon for a few minutes after each extension so long as the strain does not exceed about 4 per cent. If this strain is exceeded, the tendon becomes progressively easier to extend but its length still returns to the original value after each extension. Extensions of over 35 per cent can be reached in this way. Temperature has no effect upon the mechanical behavior over the range 0-37°C. Just above this temperature, important changes take place in the mechanical properties of the tendon which may have biological significance. The application of the techniques used here to studies of connective tissue disorders is suggested. Some of the mechanical properties of tendon have been interpreted with a simple model. I N T R O D U C T I O NMost studies of collagen h a v e been concerned with its chemical n a t u r e and reactivity, and with electron microscope and x-ray diffraction examinations with a view to determining its m a c r o and molecular structure (1-4). As yet there is no entirely satisfactory molecular model, and one major stumbling block appears to be the confusion over whether collagen is or is not capable of large extensions.A n u m b e r of measurements have been reported on the mechanical properties of such collagen-containing structures as tendons, ligaments, and fascia. T h e r e is no extensive review of the older work available. However, typical results m a y be found in references (5-7). Structures containing a high per cent of collagen were found difficult to stretch and usually broke before they elongated appreciably, while structures with a lower collagen content and a

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The relation between the glass transition temperature and the water content of wool can be described by the Fox equation. Data on transitions from a wide range of sources, including mechanical, dielectric, and calorimetric measurements, are well described by the equation. The utility of the relation for understanding and interpreting experiments on the wrinkle recovery of wool fabrics is shown.

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