As demonstrated by tests with orange and with lemon juice, the antiscorbutic vitamine is greatly protected from the destructive effect of heat when it is associated with an acid. This was shown first by Holst and Froelich and has been confirmed by numerous observers. An excellent example of marked thermostability conferred on a food by its acid reaction is furnished by the tomato, which is strongly antiscorbutic even after it has been subjected to the canning process. Conversely, Harden and Zilva have shown that the vitamine is destroyed by alkali even when dilute (one-fiftieth normal sodium hydrate) and kept in contact at room temperature; this alteration does not take place at once, but in the course of several hours. It is true that the antiscorbutic factor is peculiarly sensitive to _drying_, but there are exceptions to this rule, so that it is incorrect to state, as does the British Report of the Medical Research Committee, that "it may be regarded as an axiom that dry or dried foodstuffs will not prevent scurvy." We have shown that fresh milk dried by the Just-Hatmaker process may retain by far the greater moiety of its virtue. In this regard rapidity of desiccation and subsequent protection from oxidative processes are important factors. The general rule holds true, however, that this vitamine, in contradistinction to the "water-soluble" vitamine, is readily damaged and destroyed by drying. This vitamine is peculiarly sensitive to _aging_, especially when it is present in an alkaline or neutral medium; but even in an acid medium its potency soon diminishes. Harden and Zilva found this to be the case with lemon juice stored for a fortnight in the cold room, and our experience has been similar in regard to orange juice kept in the refrigerator under a layer of liquid petrolatum. In milk the antiscorbutic factor diminishes with age, especially following pasteurization, in the course of which most of the acid-forming bacteria have been destroyed. Aging has the least effect when the food with which the vitamine is associated has been dried. This is true not only of lemon and of orange juice as demonstrated experimentally and clinically, but even of milk, which even after it has been dried and stored for months, may still possess marked curative value.[24] [24] Reference is made to a milk dried by the Just-Hatmaker process, containing about 3 per cent. of moisture. The clinical data on which this conclusion is based are given in the previous chapter.