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associated happening in the milk diminishes the availability of these elements. Not a few studies directed to this end have been made, alike on animals and on young human subjects. The results of some of these are unconvincing owing to inadequate planning of the experiments or for other reasons, but others deserve attention and indicate that the availability of lime and phosphate is less in pasteurised than in raw milk. Quite the best series of observations bearing on this matter involved a comparison not with raw but with boiled milk (Daniels & Stearns, 1924; and Daniels, Stearns, & Hutton, 1929). It is known, however, and the fact will receive later comment, that when milk is briefly boiled and immediately cooled the changes involved are relatively slight. At any rate in observations of the kind the use of boiled rather than raw milk as a control, if of any significance, must favour the pasteurised milk in the comparison. In the carefully controlled experiments under reference, made by investigators experienced in the technique of infant feeding, comparable groups of young children, placed in precisely similar circumstances, were given equal rations of milk, respectively boiled or pasteurised by the holding process. During the experimental period it was found that the children on boiled milk showed a daily gain of lime to their bodies thrice as great as that shown by those on pasteurised milk, and a notably greater gain of phosphorus. This experiment involved a comparison that was rigorous and, it would seem, conclusive in favour of the boiled milk. It is not without confirmation from other evidence to be found in the literature of the subject (Catel, 1933; Kramer, Latzke, & Shaw, 1928; and Willard & Blunt, 1927).
76. Another circumstance calls, however, for reference here. The retention of calcium and phosphorus in the body, and their proper utilisation in bone formation, are now universally recognised to be controlled by the functioning of vitamin D (infra). As part of the above investigation other comparable groups of children were therefore given the same milk ration, boiled or pasteurised, but with the addition of cod-liver oil to increase in each case the supply of the vitamin. These latter groups showed a much greater retention of the elements in question, and only in these, even in the case of the boiled milk, did it reach the amount commonly assumed to be adequate for the proper growth of infants. Before pressing this last point further it will be convenient to make a brief general reference to the function of vitamins and the effect of pasteurisation upon them. (For an account of the literature of vitamins to 1932, see the report included in appendix 7 as Anonymous, 1932 ".)
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77. Germane to the whole question is the circumstance that the vitamin supply, whether provided by breast milk or raw cows' milk, is never in excess of the needs of the infant. In the case of the milk normally provided for the young of any species of animal, it can be understood that the amount of each vitamin is part of a general balance among the constituents of the milk as adjusted to the
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