THOMAS showed the surprising susceptibility of cartilage to the action of papain when he produced collapse of the ears of young rabbits by injecting the enzyme intravenously1,2. All cartilaginous tissue of the body was affected; the epiphyseal cartilages appeared to be particularly sensitive. Larger doses caused softening of tracheal cartilage to such a degree that some animals died from respiratory obstruction. The changes occurring in cartilage after intravenous papain were the result of a widespread breakdown of chondromucoprotein.