Perhaps the most puzzling etiologic problem of ophthalmologic pathology is that dealing with cataract. There have been advanced almost as many theories as there have been investigators in the subject. These theories have dealt with a wide range of causes, from infra-red rays emitted by molten glass to bacterial toxins. It was in the latter part of the nineteenth century, when outstanding workers on the biochemistry of the lens (such as Goldschmidt, Adams and others) were carrying on their researches that the ophthalmologic profession first gained an insight into some of the factors which involve the existence of the lens. In brief, these workers seemed to be reasonably in accord with the theory that the mammalian lens requires for its existence in its specialized state of transparency certain compounds the action of which is either directly on the cells themselves or catalytic. Another school of thought has dealt with