[Proteins, nucleic acids and acid hydrolases in the chick embryo tail bud]

During the 3d and 4th days of incubation the tail bud displays cell degeneration which result in the complete involution of both postanal gut and primitive streak. In spite of the degenerations the amounts of DNA, RNA and proteins are still growing. Over this period the activities of acid phosphatase and cathepsin are changing. The specific activity of phosphatase reaches a maximum when the tissue resorption is most intensive. The specific activity of cathepsin is then at its lowest level but it has passed earlier through a maximum.