The production of pathologic changes in the lens of a laboratory animal is one step on the road to the solution of the pathogenesis of cataract. Until recently the study of this process was possible only by the use of severe trauma to the animal. The first procedure employing dietary methods to be used as a routine was described by Day, Langston and O'Brien.1
The chance observation that a diet 70 per cent of which consisted of lactose produced changes in the lenses of rats was the origin of a series of dietary experiments. This observation on three rats revealed one immature and five mature cataracts. In following this lead a series of one hundred and seventeen rats were fed diets containing various amounts of lactose. The possibility of a deficiency of vitamin G was controlled by feeding each animal from 1 to 4 tablets of 0.5 Gm.