After the appearance of Mellanby's paper his opinion was at once accepted as resting on sound experimental evidence. The Medical Research Committee of Great Britain accepted it and gave it wide publicity in their bulletin (9). Hess and Unger (5), who had earlier stated their view that the long accepted use of cod liver oil in the therapy of rickets was based upon sound experimental data, and that in their experience it had proven a specific in the treatment of rickets, now came forward with the publication of the results of feeding experiments on infants with diets very deficient in fat-soluble A (11). The diet consisted of dried skim milk 180 grams; dissolved in ten times its weight of water; to this was added 30 grams of cane sugar, 15 c.c. of orange juice, 30 c.c. of autolyzed yeast, and 30 c.c. of cottonseed oil. This was fed to infants ranging from four to nine months of age, for a period of five to nine months. Growth at a fairly satisfactory rate was observed, and no evidences of rickets were apparent. The conclusion was drawn that fat-soluble A is a factor of minor importance in human nutrition. This view is at variance with the remarkable studies of Mori (12) and of Bloch (13) as well as of those of Wells (14), which leave no room for doubt that butter fat and cod liver oil furnish something which may under acute conditions cause prompt recovery from ophthalmia, brought on by malnutrition.

The diet employed by Hess and Unger cannot be regarded as a satisfactory one to which an infant may safely be confined, notwithstanding their observation that their subjects grew during the experimental period. There is every reason to suppose that they were brought into a state of nutritional instability as the result of being confined to the diet. This was very satisfactorily constituted except for its shortage of fat-soluble A, and judging from experience with animals they should, therefore, have been able to tolerate for a considerable period this defect in their dietary, but not necessarily without injury in some degree. McCollum and Davis (15) had shown that skim milk powder contains approximately half the fat-soluble A that was contained in the whole milk from which it was prepared. Hopkins (16) has expressed a similar view as the result of his investigations. No conclusions are warranted from the data of Hess and Unger other than that young children can live and grow as their graphs show them to have done. They throw no light on the relation of fat-soluble A in its relation to bone growth, or the nutritive needs of the human infant for this dietary factor, since their experimental diet was by no means so deficient in fat-soluble A as they supposed it to be.

Very recently Hess and Unger (17) have abandoned the view that rickets is due to dietary defects, and have adopted the view that hygienic factors, especially sunlight, play a dominant role in determining the seasonal variation of this disorder. They base their belief upon the evidence afforded by rontgen ray pictures, which showed that illumination of infants suffering from rickets, with ultraviolet rays from a mercury vapor lamp, caused the deposition of calcium phosphate in the zone of primary calcification of the long bones. Hess and Unger offer no explanation for the mechanism of the action of cod liver oil as a specific therapeutic agent in the treatment of rickets in their earlier studies.