Experimental cataract is most easily produced in young growing animals, and, indeed, some types can be produced only in the very young.1 Any attempt to identify the initial chemical events associated with cataract must depend upon a precise knowledge of changes which occur as a function of normal growth and maturation. Early investigators were well aware that the composition of the lens changes rapidly with growth, and the fact was recognized in comparing cataractous lenses with normal controls of approximately the same age.2,3 However, no systematic study has been done which would establish the statistical variance for any component of the lens at any stated age of the animal. In the absence of such information, presumed differences must be large in order to be convincing and even then are open to the question of analytical error. The present report is drawn from a large body of data which