MUCOID SALTS.

We know practically nothing about the ways in which proteins are held in living protoplasmic structures. The molecules of the protein compounds are relatively so large that as yet our physicochemical methods of measurement are inadequate to give us correct ideas of molecular size and intramolecular structure, although we know considerable about the lifeless and, in some respects, comparatively meaningless fragments into which protein molecules may be broken. Our ignorance of the fundamental biochemic relations of proteins to the associated constituents of protoplasm appears to be largely due to our vague knowledge of the chemical statics and dynamics of true cellular proteins, a fact which serves as a constant stimulus to protein investigation.

Among the many protein substances the nucleoproteins and the glucoproteins are very important tissue constituents. The essential part of each natural type of these proteins, and the part to which the usual name is applied, appears to