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INTRODUCTORY NOTE In a paper published by one of us thirty years ago (Hopkins, 1912), experiments were described showing the marked effects of very small quantities of milk in promoting growth in rats on diets which otherwise contained no vitamins. At the time of these early experiments such factors as refection and the effects of coprophagy had not been recognized, while the large number of nutritional factors now known to contribute to normal growth was unsuspected. It seemed worth while, therefore, when the opportunity arose to attempt to define more closely the conditions necessary for the milk effect. As a matter of fact we have found little difficulty in reproducing the original results. Our experiments, however, have revealed some fresh facts and relations to which we feel attention should be called. Since Fridericia (1926) first described refection many workers have supplied abundant evidence for the reality of this nutritional condition. Even to-day, however, it cannot be said that its causal relations are clear. It is remarkable that in dietaries capable of evoking the refected state the nature and condition of the carbohydrate supply should play so significant a part. Those who have had first-hand acquaintance with the facts all agree that refection does not occur except when the experimental diets contain raw starch. When the .carbohydrate supply is starch dextrinized or cooked, or when soluble sugars replace the starch, refection is never observed. This fact was from the first emphasized by Fridericia himself. Our own experience is fully in accord with that of others. In this laboratory we have, moreover, always found it necessary to employ raw potato starch. When this has been replaced by raw rice starch we had never observed a case of refection on diets free from the vitamins of the B complex until a later date in circumstances which will eventually be discussed, but this has not been a universal experience. Indeed, Fridericia's pioneer studies of the phenomenon were made with rice starch though it would seem that relatively few of his animals developed refection. Miss Roscoe (1927) J. Hygiene 44 also saw refection established on a rice starch diet, as also did Dr Harris at the Dunn Nutritional Laboratory at Cambridge. On the other hand, Kon & Watchorn, working in this laboratory so far back as 1928, could only be sure of establishing the condition by substituting potato starch for the rice starch then ordinarily used for the synthetic basal diet. During more recent years more than one worker has performed experiments in Cambridge . involving the use of dietaries deficient in the B vitamins, but no one has reported the establishment of refection when the carbohydrate supplied was raw rice starch.' It would be surprising if this were a wholly local circumstance, but Kon (1931) has reported that he found the same difference between these starches when working in three other laboratories, at Warsaw, Berkeley (California), and Reading. It is further noteworthy that all later workers on the subject in America have, for whatever reason, employed potato starch when wishing to obtain refection.

On refection in rats and on the nature of the growth promoted by the addition of small quantities of milk to vitamin-free diets