The knowledge of the chemical composition of most tissues is yet unsatisfactory. A few organs have been studied intensively, and their composition is relatively well known ; on the contrary, for many other organs systematic data are still lacking. To undertake a study of physiologic chemistry before having a sufficient knowledge of "anatomic chemistry" results in incomplete or even false interpretations.
The analyses of the ocular tissues are fairly complete. This is particularly true for the lens. For 100 Gm. of lens, the composition of about 98.5 Gm. is known. The remaining 1.5 Gm. contains substances which, acting as catalysts, play an important role in spite of their low concentrations. Other substances enter the lens by diffusion ; they do not act as metabolites, and their role is unimportant. But although the unknown fraction of the lens is a small part of the total weight, investigation of it may reveal the presence