The purpose of this research was to study the mechanical properties of the anterior cruciate ligament of canines. The changes in the shape and magnitude of the stress-strain curves for various strain rates are discussed in detail. The specimens were tested in tibia-anterior cruciate ligamentfemur preparations which were subjected to environments of moistening and direct immersion in a saline solution. For these tests the specimens were constrained in the normal flexed positions of the hind limbs of canines. Information dealing with the per cent cumulative stress relaxation was obtained by allowing the specimens to relax at regular intervals during the loading. By testing each of the specimens twice, information regarding the possible damage, which might have occurred during the first test cycle below 10 per cent strain, was obtained.

The stress-strain data fitted extremely well with an exponential relationship suggested by Y. C. Fung for the mesentery of the abdomen of a rabbit. The variation in environments appears to have an effect on the properties of the ligament. The results of the relaxation tests indicate that for high values of stress the per~cent cumulative relaxation is linearly proportional to the value of stress. It was observed that when 2 successive tests below 10 per cent strain were subjected to the same specimen, the second resulting test shows an extended initial toe region. However, in the linear region of the curves the slope is almost identical with that of the first test.