The fluorine contents of a number of draught and bottled beers from various sources were in the range 0·15‐0·86 p.p.m. and are considered unobjectionable. Of the brewing materials examined, malts usually proved rich in fluorine (< 0·2–11·8 p.p.m.), though barley samples contained < 0·2 p.p.m.; it is suggested that the high values in malts may be due to fluorine derived from coal. However, the bulk of the malt fluorine remains with the spent grains.

Nutrient agar (pH 7·4) was, in general, used for the tests, as wort agar (pH 4·85) allowed excessive growth of yeasts and moulds which suppressed bacterial development. Open exposure of plates to compressed air causes entrainment of organisms from the atmosphere, giving falsely high results. With appropriate shielding of the plates, however, this difficulty can be avoided, though care must be exercised in the choice of shielding device, or low results may be obtained as a result of imperfect deposition; a modification of the Hollaender & Dalla Valle apparatus (Publ. Hlth. Rep., Wash., 1939, 54, 564) is preferred for comparative routine tests. If it is desired to use a filtration method, calcium alginate wool may be used as collecting medium, being thereafter dissolved in sodium hexametaphosphate solution as a preliminary to plating.

The possible fluoridation of public water supplies as a means of controlling dental caries raises the question of the influence (if any) which such a proceeding would have on yeast and fermentation. Previous work is briefly reviewed, and experiments are outlined to illustrate the effect of varying amounts of fluorine on fermentation, the quantity of fluorine taken up by the yeast, and the possibility of stimulation by very small additions. A comparison is made of two sources of fluorine and the possible cumulative effect at low concentrations is also studied. It would appear that, at the concentration likely to be employed (I p.p.m.), there would be no effect on yeast activity.

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