When a practical feeder, trained In the school of experience, asks, "What are vitamines, anyway?" and "What do these rat-feeding experiments have to do with feeding pigs?" he deserves a fair answer. While the study of vitamines In the experiment stations has uncovered facts of much value to the livestock man, It Is possible for those who are over-enthusiastic to emphasize too highly In some cases the Importance of vitamines to animals red under average conditions. It Is essential to discover where emphasis should be laid upon vitamines under practical feeding conditions.