Publisher Summary S.V. Perry started his career in muscle biochemistry in 1946. An aim of my thesis work was to try and understand the nature of the interaction between actin and myosin and the remarkable effects of adenosine triphosphate (ATP) on it. Later by the use of iodoacetate, he was able to show that if the ATP stores of the muscle were depleted, “thaw rigor,” as S.V. Perry called the phenomenon, did not occur. The shortening was a result of the uncontrolled effect of ATP on the myofibrils in the muscle cell disorganized by low speed freezing. This disrupted the sarcoplasmic reticulum, allowing the stored calcium to leak out on thawing and trigger off the actomyosin ATPase. Another striking feature of thaw rigor was a loss of about 35% of the muscle weight because of the extrusion of fluid that accompanied the shortening process; a process similar to the synaeresis that occurs when actomyosin suspensions are treated with ATP.