It should be evident from what has already been said that the importance of the vitamins, especially in early life, can hardly be overemphasized. Apart from the specific diseases, scurvy, xerophthalmia, and perhaps rickets, which result from pronounced deficiency of these factors in the diet, there is a long list of less obvious disorders which might easily be ascribed to some other cause, or even escape notice altogether for a considerable time, but which are probably as inevitable accompaniments of a diet poor in vitamins as are the recognized "deficiency diseases " themselves.1 Schaefferla believes the avita-minosis (vitamin deficiency) of young infants the most common of all and the most difficult to differentiate. Besides the marked decline and wasting of the tissues, frequently accompanied by xerophthalmia, which are regarded as indications of lack of A, diminished appetite, weakness, and lack of resistance to infection, anemia, and sometimes diarrhoea develop on diets which are inadequate in respect to this factor. Growth may be retarded, even where the deficiency is not so pronounced as to lead to actual wasting of the tissues.

Derangement of the calcium metabolism is, according to Mellanby, a serious result, which may be manifested in the appearance of rickets and the production of defective teeth. Puppies which had been brought up on such a diet developed irregular and overlapping teeth, with the enamel partially lacking or very defective, the teeth in many cases being soft enough to be cut with a scalpel.

Deficiency of B leads to functional changes of almost all the organs of the body as well as to degeneration of the central nervous system. The glands of internal secretion and the digestive organs appear to suffer particularly. Acidosis frequently results from imperfect carbohydrate metabolism. McCarrison believes that many of the obscure diseases of children may be directly or indirectly due to lack of this vitamin. Moreover, deficiency of B, as of A, leads to lowered resistance and increased susceptibility to bacterial infection. Loss of appetite is one of the earliest symptoms and a very serious one, since it results in diminished intake of food and hence still greater deficiency of vitamins.

1 See Ch. IX.

1a Schaeff er, Medecine (Paris), 1, 728, 1920.

Lack of C is followed by the appearance of scurvy in a comparatively short time, but Hess in America, and Barton2 have warned practitioners that the external symptoms of this disease indicated the later stages of deficiency, and that various ill-effects may have been developing slowly for some time. They therefore recommend the administration of antiscorbutic as a routine practice with all artificially fed infants, even where these are apparently healthy, a practice which has been advocated by Pritchard 3 also.

The calcium metabolism suffers from lack of C as well as from deficiency of A, resulting in abnormalities of the bony structure and of the teeth. It has been found possible to produce a condition in the teeth of guinea pigs closely resembling, if not identical with pyorrhea in man, by depriving them of adequate supply of C, and there is fairly convincing evidence for the belief that the defects of the teeth which are so prevalent in the present generation are due to insufficiency of vitamins in the food.

It is therefore of the utmost importance that the growing child be abundantly supplied with the necessary factors from early infancy.

The natural food for the young mammal is the milk of its mother. The variations in the milk of different species appear to be such as will correspond to the specific needs of the young of that species, and it may be assumed that the milk of a healthy mother on an ample and well-balanced diet will fully satisfy the physiological requirements of her offspring until it is ready for weaning. On the other hand, as has been pointed out already, if the diet of the mother is deficient in any respect, normal growth of the young can take place for a limited time only. Among the poorer classes in the Philippines, where the principal food is rice and fish, infantile beriberi is common among breast-fed children, and Andrews demonstrated that the milk of the mother of these children would produce antineuritic symptoms in puppies when given as the sole source of vitamin B. Scurvy, rickets, and pellagra have all been observed in breast-fed children, although such observations are rare compared with the number of cases among infants on artificial diets.

McCollum and Simmonds4 made an elaborate study of the effect produced upon the offspring by depriving lactating rats of definite dietary factors.5 Where the mother's food was entirely lacking in A growth took place at subnormal rate, indicating either that the young rats had a reserve store in their own tissues or that the mother was secreting a small amount of this vitamin from her own body fat. That the latter hypothesis is the correct one is indicated by the loss of weight by the mother. McCollum says: " It seems certain that the body fats of an animal which has been fed for some time on a diet rich in this substance A, will serve as a reserve supply of this dietary essential which the mother can secrete into the milk".

2 Barton, Lancet, 1919, ii, 348. 3 Pediatrics, 26, 300, 1913.

4 McCollmn and Simmonds, Am. J. Physiol. 46, 275, 1918; McCollum, "Newer Knowledge of Nutrition," N. Y. 1919, 117.

5 See also Drnmmond, Lano. 1918, ii, 482.

Experiments with diets deficient in B gave similar results, and McCollum concluded that neither A nor B is present in the optimum amount in the milk of the mother unless they are supplied in her food. Since, however, the young grew for a considerable time, although at slightly subnormal rate, when the mother was on a diet which would not sustain any growth in the young after weaning, it is evident that the mother can produce milk which is an improvement in respect to vitamin content, over the ration which she is herself receiving, either by concentrating in the milk the small store of vitamins which she gets, or by using up the reserve store in her own tissues. She is thus, as McCollum points out, a factor of safety for the nurslings. Similar observations were made in other experiments in which the diet was deficient in protein or mineral salts. While a certain amount of growth was possible, - in some cases a surprising amount, - both the young and the mother suffered. Commenting upon these experiments, McCollum remarks: 6 "The statement which one sees reiterated so frequently, that breast feeding of infants is superior to the best system of artificial feeding, needs to be qualified to some extent.

There are, without question, in many parts of the world, large groups of people whose diets are of such a character that the quality of the milk produced by the lactating mother is not such as to make it a satisfactory food for their infante.6a It should be thoroughly appreciated that the human mother should have in her diet a liberal amount of milk in order to safeguard the health and well-being of her infant, and of leafy vegetables, which serve the two-fold function of a protective food and of greatly aiding intestinal elimination. That some mothers can induce a fair amount of growth in their infants while taking a faulty diet, cannot be denied, but that both mother and child suffer impairment as the result is beyond question. It is not enough that the diet shall furnish enough calories and enough protein, and shall afford variety and palatability. The peculiar dietary properties of the foodstuffs which enter into the diet are of paramount importance, and must be taken into consideration".

6 McCollum, " Newer Knowledge of Nutrition," p. 128.

6a From experiments conducted with rats, Hartwcll (Biochem. J. 15, 140, 1020) has ascertained the effect of diet on mammary secretion. Provided the mother is given a good diet such as bread and whole milk, the baby rats at the end of the lactation period will weigh twice as much as when the mother is supplied with a poor diet, i. e. bread only. Extractives and protein tend to keep up the mother's weight. An excess of protein after a time brings about a cessation of the milk supply. Neither absence of fat nor an excess of carbohydrate appeared to have a disturbing effect. During the normal period of lactation, the mother can furnish vitamins A, B and C.