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typical acute scurvy, were proved to be scorbutic by the fact that they cleared up immediately when the fruit juice ration was restored. It may be claimed, moreover, that what has been called latent scurvy in infants is not very uncommon, and up to a few years ago, before research had focussed attention on the importance of quali- tative defects in food, its nature was seldom recognised. It is a condition in which a group of somewhat obscure symptoms disappear at once when an anti-scorbutic is given. Such cases mostly occur in Reference to this clinical experience large towns (Hess, 1920). introduces a consideration which should not be ignored. It is logical to suppose that a food deficiency which, when complete or extreme, results in a recognisable disease may, when less complete, be This responsible for minor but significant degrees of ill-health. possibility can only be ruled out when the minimal needs for the variable factors are quantitatively known, and known to be adequately supplied. It is sure that obscure or sub-acute symptoms really due to nutritional errors are still not infrequently attributed to other causes than the right one. Yet such minor degrees of malnutrition main- tained throughout infancy may leave a permanent impress upon later development. Such in milk-fed babies may, of course, be due to reasons which have nothing to do with the pasteurisation of the milk supply.
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93. If it must be admitted that certain nutritional faults may fairly be ascribed to properly pasteurised milk, it is as unjustifiable to exaggerate their practical importance as it would be erroneous to ignore their existence. Any defects in nutrition which may follow upon its use would, with present knowledge, seem to be minor in degree, limited in kind, and when recognised, very easy to correct. More significant still is the fact that by simple addenda to the dietary they can be prevented.
94. An unprejudiced survey of the evidence available to-day will leave on most minds a conviction that any recognisable changes of quality induced in milk by pasteurisation rightly conducted are as a whole too small to outweigh the great advantage inherent in the protection from infection which the treatment secures and in the public confidence which it inspires. It is sometimes suggested that there may be subtle changes not revealed in the state of present knowledge. Policy cannot justifiably be influenced by vague possibilities which established evidence makes improbable. Nevertheless, that the functions of vitamins C and D are indispensable has been abundantly demonstrated. It is sure that nutrition is no longer normal when the supply of these is below a safe minimum which, for the human infant, is not yet accurately defined. It is highly desirable, there- fore, that the bottle-fed child should be protected from possible deficiencies in these health factors, but from what has been said earlier in this discussion it will be admitted that such protection is almost as necessary in the case of raw milk, with its variable vitamin content, as in that of pasteurised.
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95. The custom of supplying fruit juice to milk-fed children would seem now to have become common, though not universal (see paragraphs 99 to 101 below). While this practice is desirable, whatever the milk supply, any policy leading to an increase in the pasteurisation of supplies should perhaps call for increased educational efforts on the part of all concerned with the health of infants to make it general. During the winter it is almost equally desirable that cod liver oil should be administered in small amounts to infants reared on cows' milk.
96. A few words will suffice for reference to the effect of other forms of heat treatment. Animal feeding experiments, as well as certain laboratory results, have shown that milk brought quickly to the boiling point in a covered vessel and immediately cooled undergoes but slight changes (Schwartze, Murphy, & Hann, 1929-30; Munsell & Kifer, 1929; and Barnes & Hume, 1919), and this would seem to be confirmed by the results of its use in infant feeding. On the other hand, there is much evidence to show that the temperature used in pasteurisation (145°) if maintained must not be exceeded. Changes become rapid at temperatures only a few degrees higher. Sterilisation, that is to say prolonged treatment by heat above the boiling point or at temperatures near to it for the complete destruction of bacteria, produces, as might be expected, changes similar in kind but more extensive than those due to pasteurisation. No adequate comparison between the relative nutritional value of sterilised and pasteurised milk has been made in actual practice, but the former is now unlikely to be much used in infant feeding.
97. There is evidence to show that milk, when repeatedly subjected to heat treatment of any kind, undergoes progressive deterioration as a food.
98. The bibliographical references to the papers referred to in this sub-section will be found in appendix 7. A full and critical account of the properties of milk in relation to pasteurisation with references to the relevant literature has recently been published by Stirling and Blackwood (1938).
(e) The extent to which a supplementary diet is fed to children whose main diet is milk.
99. It is of importance to the issues raised in this discussion to discover if possible how far the use of anti-scorbutics in infant feeding has become general. The following information is due to the kind offices of Dr. Frank Robinson, medical officer of health for the county of Cambridge, and through him to kindness of the medical officers of three other counties, Gloucestershire (Dr. Middleton Martin), Wiltshire (Dr. C. E. Tangye), and Durham (Dr. C. Franks).
100. In these four representative counties a questionnaire was distributed to health visitors and district nurses, asking with regard to the homes visited by them: (a) whether the cows' milk fed to
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