Abstract CALVERY 1 has shown that the protein of egg shell membranes has the amino acid composition of a typical keratin. An additional protein exists in the mineral portion of the shell and appears to serve as a matrix in which the inorganic salts are imbedded (Nathusius 2 ). An investigation of this matrix protein has been made in order to classify it more definitely. Eggs were thoroughly scrubbed with salt solution, broken and the shells thoroughly washed out. The shells were decalcified in dilute hydrochloric acid and the shell membranes removed. The remaining material was washed several times with salt solution and distilled water by centrifuging. The shell membranes were given a similar treatment. The materials were then dried in a current of air at 37° C and characteristic protein tests applied to each. The percentage of membrane in whole egg shell has been given by Almquist and Burmester 3 as 4.75, a mean . . .