A new method for determining the composition of the colloidal phosphate of milk has been developed, based on analysis of milk free from colloidal phosphate. Preparation of this material is described.

The results suggest that the so-called colloidal calcium phosphate of milk should be more properly described as a colloidal phosphate—citrate.

This colloidal phosphate—citrate shows considerable analytical resemblance to the precipitate formed on neutralizing acidified milk serum. Both can be represented approximately by the empirical formula of a hypothetical citrate apatite.

Data available for fifty cows mainly infected with Staphylococcus pyogenes have been analysed to determine the effects of udder infections and mastitis on milk, fat and solids-not-fat yield and on fat and solids-not-fat percentages over full lactations.

It was found that lactation yields of milk, solids-not-fat and fat were depressed by 10, 11 and 12% respectively in the presence of infection. These depressions were significant (P < 0·05). The composition of the milk averaged over whole lactations was not significantly affected (P > 0·05), although the mean solids-not-fat percentage of the milk was significantly depressed by 0·196±0·092 during the period of infection.

It is suggested that the depressions in lactation yield and changes in milk composition would have been greater in the absence of antibiotic therapy for mastitis.

Dried skim-milk stored at 55°C in air at 70% relative humidity has been found to contain lactulose, galactose, tagatose, glyceraldehyde and maltol; and formic, acetic and glycollic acids. These compounds are not present, or are present only in trace quantities, in fresh dried skim-milk. It is suggested that while the proteinsugar reaction is responsible for most of the browning of the powder, many of the compounds found are formed by degradation of lactose catalysed by the free basic amino groups of the casein. The compounds so formed probably then react with amino groups in a Maillard reaction and thus contribute to the browning of the milk powder.

The effect of ultra-high-temperature (U.H.T.) sterilization and of subsequent in-bottle sterilization on the availability of milk calcium has been studied in experiments with rats. The heated milks and the raw milk from which they were prepared were freeze-dried and added to a diet low in Ca so that the resulting diets contained some 0·11% Ca and 0·42% P.

Ca retention by groups of six litter-mate male weanling rats was 98·4, 98·4 and 98·5% respectively from diets containing raw milk, U.H.T.-treated milk and milk treated by U.H.T. followed by in-bottle sterilization. It is clear that these processes did not affect the availability of milk Ca.

The diet and milk from a herd of dairy cows were analysed regularly for 90Sr and calcium. The ‘observed ratio’ (the ratio of 90Sr to calcium in the milk divided by the ratio of 90Sr to calcium in the diet) was found to be 0·10 against 90Sr in favour of calcium, which corresponds well with the results of other workers. The amount of 90Sr secreted into the milk was 1·2% of the total ingested. Similar values were obtained using stable strontium data.

Soil samples from different depths and herbage were taken from three areas with different cultivation histories and analysed for 90Sr and calcium. The effect of ploughing on the vertical distribution of 90Sr in soil and on the 90Sr levels in vegetation was examined.

Seven strains of Streptococcus cremoris, four strains of Str. lactis, and one strain of Str. diacetilactis were examined for their ability to produce aldehydes and methyl ketones when grown in skim-milk. All strains were found to produce acetaldehyde and seven also produced acetone. No other aldehydes or methyl ketones were detected in any of the cultures.

A method for the quantitative estimation of mixtures of aldehydes and methyl ketones by means of paper chromatography of their 2,4-dinitrophenylhydrazones is described.