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when an iron salt was present in amount equal to 9 milligrams (one-seventh of a grain) of the metal per gallon, the loss was 39 per cent.; in the presence of copper at an equal concentration the loss was 79 per cent. In (b) the milk by itself lost 20 per cent.; with the above concentration of iron, 29 per cent., and with copper, 80 per cent. The copper is much the more active catalyst, and during the times of exposure to heat induces large destruction even when the available oxygen is only that which is dissolved in the milk itself. Aluminium and nickel are apparently without any such action (Schwartze, Murphy, & Cox, 1931).
84. It should not be forgotten that fresh untreated cows' milk in the amounts normally consumed contains a supply of this vitamin no more than barely adequate for the needs of the infant, and from cows not on pasture it may at times be inadequate. The further reduction due to heating, if uncorrected, may therefore be serious. Fortunately a correction for any deficiency is easily made by the administration of the juice of citrus fruits, oranges or lemons, now so easily obtainable throughout the year, or even of the juice expressed from scraped swedes and (less potent) from raw potatoes. In any of these the concentration of the vitamin is out of all proportion greater than in fresh milk. Few will deny to-day that such additions to the food of infants are desirable, whether they are consuming pasteurised or raw milk.
85. The remaining known vitamins require less attention in this discussion. Some have functions remote from those affecting infant nutrition.
86. A supply of vitamin A is necessary for the promotion of growth and the maintenance of health. Cows' milk, however, contains it in relatively large amount, and though it is destroyed when heated in the presence of oxygen, there is no evidence that pasteurisation has anywhere been directly responsible for such nutritional disorders as are known to follow upon lack of this vitamin.
87. Several vitamins with distinct functions are comprised in what has become known as the "B complex." Of these, only two, B, and B2, call for reference here. B,, which is concerned in main- taining normal conditions in the nervous tissues is present in relatively small amounts in milk, and it is not resistant to heat. Nevertheless, though symptoms attributed to B, deficiency in the milk supply have occasionally been observed in infants and proved to be curable by giving yeast preparations as a source of the vitamin, no evidence has come to light showing that pasteurisation has by itself been responsible for such conditions. B,, of which a deficiency leads to the disease pellagra, is relatively abundant in cows' milk and is resistant to heat at higher temperatures than those involved in pasteurisation. It may be said with some assurance that in connection with nutrition of children, the only vitamins of which a deficiency in milk is serious are those known as C and D.
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88. This brief review of available knowledge indicates that the only effects of pasteurisation of milk which call for serious considera- tion are, diminished availability in its lime and phosphorus, and a lessened anti-scorbutic power. The practical importance of these defects calls for some closer appraisement.
89. It is perhaps only in relation with infant feeding that they can possess significance. Older children seldom depend on milk alone for their supply of the vitamins C and D, and the benefit of a milk ration when added to the average diets consumed say by children in institutions, while unmistakable and even unexpectedly great, would seem to be exerted by pasteurised no less than by raw milk (Mann, 1926). The acid test for any significant nutritional faults in pasteurised milk must be sought in its effects upon infants when it is fed to them without additions.
90. With regard to the effect of the treatment on the minerals of the milk, if it results in nutritional errors, an increase in the liability of infants to rickets would be the most likely indication of these. As already remarked, while minor degrees of rickets are common among infants to-day, cases of the acute or florid disease, leading to chronic conditions and to permanent bone deformities, are in most districts much less common now than they were a generation ago. This is doubtless due to a general improvement in the methods of feeding infants, together with the custom-essentially modern of taking them freely into the open air, and thus inciden- tally exposing them more frequently to sunlight. There is no clear evidence that the disease shows less signs of abatement in districts where the greater part of the milk supply is pasteurised than in others where it is not.
91. With regard to scurvy, although there is such abundant evidence to show that the disease inevitably follows when adolescents and adults are deprived of vitamin C for periods sufficiently long, and that cases were frequent among infants in post-war Europe, yet nowhere in this country to-day is overt infantile scurvy other than a rare disease.
92. It was, however, apt till lately to appear in institutions, and probably it is only the typical clinical picture of the established disease that is so rarely seen. It is at any rate noteworthy that
well attested observations have shown that minor and less easily recognisable symptoms of scurvy may on occasions arise when pasteurised milk is fed alone. At a large clinic in New York, for instance, infants when fed on it were customarily given a ration of fruit juice and were free from scurvy. When an American investiga- tion committee had reported that the nutritional value of pasteurised milk was apparently equal to that of raw milk, the fruit juice was for a time given up. As a result a large proportior of the children came to display untoward symptoms which, though not those of
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