An extremely interesting observation was made by Steenbock and Gross (1) in 1919. They discovered that carrots and yellow sweet potatoes are relatively rich in the substance fat-soluble A, whereas red beets, parsnips, rutabagas, sugar beets, potatoes, mangels and dasheens are very poor in it. Steenbock and Boutwell (2) found yellow maize a sufficiently good source of the fat-soluble A to support approximately the average amount of growth in a male and a female rat when this cereal formed 83 per cent of the diet, and when it was satisfactorily supplemented with respect to inorganic deficiencies. The male appeared rough-coated after the age of eight months. The female produced ten litters of young. The first eight of these all died a few days after birth, but the last two litters were reduced to three and four young, respectively, and were satisfactorily nursed to a state of independence by the mother. White maize, on the other hand, was found without exception to be very deficient in this dietary factor, although several varieties were tested. Animals which derived a large part (85 per cent) of their food from white maize failed to grow beyond a very limited degree and suffered from xerophthalmia and debility of the skin as shown by incrustation of the ears, warts on the nose, infections of the tail and feet, and sores on the body. These skin conditions are apparently due to lack of resistance of the skin to invasion by an itch mite, although Steenbock and Bout-well make no mention of this. McCollum and Simmonds, in their earlier experience frequently observed these conditions in poorly nourished rats, and microscopic examination of material from the lesions revealed the presence of large numbers of very small mites. In recent years, they have been able to eradicate this parasite from their colony, and the lesions described by Steenbock and Boutwell have entirely disappeared. Such skin conditions are not, therefore, to be regarded as in any way associated with this type of specific starvation.

Red maize, which was free from yellow pigment was likewise found to be free from fat-soluble A, whereas red maize which contained yellow pigment proved a fairly good source of this substance. Variegated maize, in which the pigments were irregularly distributed and which on that account contained red, yellow and blue pigmented portions, as well as some white areas, gave results in feeding experiments which were intermediate between white on the one hand and deeply yellow pigmented varieties on the other. Where yellow kernels occurred mixed with white in variegated ears, a selection of the two kinds showed by appropriate tests that the former contained distinctly more fat-soluble A than the latter.