If then a factor or factors essential to growth be missing from, or deficient in, a dietary, the consequent arrest of, or diminution in, growth energy may diminish the instinctive consumption of food, while the supply of such factors may increase consumption as an indirect result of a direct affect upon growth.

Karr 58 found that feeding dogs on a diet very deficient in vitamins resulted in decreasing appetite to the point of ultimate refusal to eat at all, unless vitamin was added. He states that a rather definite minimum amount of vitamin B seems to be necessary to sustain the desire to partake of food which is otherwise adequate for the nutrition of the animal. The actual amount of vitamin required varied with different animals, 0.5 g. of brewery yeast for instance being sufficient for some, while others required three times as much. That lack of vitamin is the direct cause of the failing appetite was shown by the fact that there was no such failure when the requisite amount of vitamin was given from the start as an addendum to the diet.

58 Karr, J. Biol. Chem. 44, 255, 1920.

Cowgill58a has confirmed the observations of Karr, and demonstrated that alcoholic extracts of wheat embryo, rice polishings and navy bean contain the appetite-promoting factor.

In addition to the well-known symptoms of scurvy resulting from deficiency of C, McCarrison59 has noted the following results determined from the histological examination of guinea pigs which had been kept on a diet of crushed oats and autoclaved milk: The size and weight of the adrenal glands increased, accompanied by degenerative changes in the cellular elements of the adrenal cortex and medulla and marked diminution of the adrenaline content. The bladder showed congestion of the mucous and muscular coats and degenerative changes of the epithelium, with hemorrhagic infiltration. In many cases there was considerable enlargement of the thyroid, the result in the main of congestion and hemorrhagic infiltration of the tissues.

A connection between calcium metabolism and the vitamin content of the diet is indicated by the work of several investigators. Mellanby60 concluded from his study of puppies that substances containing and associated with A are particularly concerned in the calcification of the bones and teeth, a point of view which is confirmed by the work of Shipley, Park, McCollum, Simmonds and Parsons,61 who found the cartilage and adjacent portions of the metaph-sis of the long bones of the extremities of rats could be rendered entirely free from calcium by feeding diets low in A. After about 40 days on this ration, when the symptoms characteristic of lack of A were well developed, two per cent of cod liver oil was incorporated in the diet, with the usual beneficial effects. After a few days the animals were killed and their bones compared with those of control animals which had received no oil. While no gross differences could be detected, microscopic examination showed that those to whose diet the oil had been added showed a line of freshly laid down lime salt in the matrix of the proliferative zones, while the epiphyseal cartilages of the controls were calcium-free. Telfer61a on the other hand states that an experiment with an 8-months-old infant on the influence of cod liver oil and butter-fat on the retention of calcium and phosphorus gave no support to the theory that these substances in the diet specifically affect calcium retention.

58a Cowgill, Am. J. Physiol. 57, 420, 1021. 59 McCarrison, Ind. J. Med. Res. 7, 188, 284, 633, 1920. 60 Mellanby, Proc. Soc. Physiol. J. Physiol. 52, liii, 1919. 61 Shipley, Park, McCollum, Simmonds, and Parsons, J. Biol. Ghem. 45, 343, 1920.

61a Teller, Proc. Physiol. Soc., J. Physiol. 54, cv, 1920.

It is believed by some observers that other vitamins besides A may be concerned in the deposition of calcium. McCarrison notes that lack of B causes thinning of the bones and decrease in the bone marrow. Rarefication and fragility of the long bones and enlargement of the junctions of the ribs and cartilages are commonly reported as symptoms of scurvy resulting from deficiency of C.

The recent work of Mellanby62 and Howe63 on the connection between tooth formation and the vitamin content of the diet is of! great interest. According to Mellanby, a diet, containing an abundance of food with which A is associated, allows the development of sound teeth in puppies.

A diet otherwise adequate but deficient in such substances brings about the following defects in puppies' teeth: delayed loss of deciduous teeth, delayed eruption of permanent dentition, irregularity in position and over-lapping, especially of incisors, partial absence of or very defective enamel, and low calcium content. The deficiency in calcium salts may even result in teeth being so soft that they can be cut with the scalpel. The evidence makes it clear that this is an instance of diet affecting the teeth from inside and is independent of bacterial sepsis and other conditions associated with food. These results cannot be considered as due to acute illness of malnutrition, for the improvement of the teeth on adding substances containing A is as characteristic as the deleterious effect of the deficient diet, and there is evidence that the defective teeth are most pronounced in rapidly growing puppies.

62 Mellanby, Lancet, 1918, li, 765.

63 Howe, Dental Cosmos, 62, 636, 1920; J. Home Ec.

Mellanby points out that the crowns of the deciduous teeth of children are for the most part developed before and during the first few months after birth. In order to supply the offspring, the mother must have an adequate supply of A in the diet.