1. Some questions concerning the interpretation of observations on milking dairy cattle are considered.

2. A formula is presented for analysing the contributions of changes in the numerator and denominator to the changes in a percentage or fraction, and the formula is applied to changes in the composition of milk.

3. The depressions of the butterfat and solids-not-fat percentages consequent on diets reduced in hay in a dairy-cattle feeding experiment are examined with this constituent analysis.

The contributions of changes in the magnitudes of the aqueous, butterfat and solids-not-fat constituents to the difference between the butterfat percentages of cows on two treatments, 18 lb. hay/day (control) and 6 lb. hay /day, are about equal. There is an apparent qualitative difference between the effects of the two non-control treatments, and a reduced yield of butterfat would alone largely account for the lower butterfat percentage of cows on the 2 lb. hay /day treatment.

The milk-ejecting activity of the hormones of the posterior-pituitary gland is well known and has been adequately reviewed (1). Most of the published information deals with the lactating dairy cow. In the course of work at this Station involving the lactating sow as a basis for assay of the milk-ejecting hormones (2, 3), data have been collected on the effect of a standard dose of oxytocin. Our normal assay procedure (2) involves giving the animal a preliminary dose of 0·5 unit of oxytocin. Thus over one lactation we have been able to record the time between injection into the ear vein and the onset of milk let-down, and the period during which milk may be obtained by simple hand-milking, for a number of sows. Braude & Mitchell (4) have published figures for the milk let-down effects of doses of oxytocin ranging from 1 to 10 units. The following results were obtained with &5 unit. All sows used were of the Berkshire breed.

Eleven Shorthorn cows were milked for 14 days before their expected calving date. The total amount of prepartum secretion varied, between cows, from 1 to 961.

Determinations of total solids, fat, solids-not-fat, lactose, total protein, ash, calcium, phosphorus, chloride, casein, albumin, globulin, proteose-peptone, N.P.N., vitamin A and carotenoids were made regularly on the secretions of eight of these cows during the prepartum period, and for 4 days postpartum; and, for comparison, on five samples of Short-horn colostrum each representing the total secretion obtained from the two milkings within the first 24 hr. after calving.

It has been found that when three strains of Bacillus cereus are grown in turn with each of two strains of Streptococci lactis and two strains of the coli-aerogenes group, the growth of the spore-formers is neither suppressed nor stimulated. It has been confirmed, however, that the spore-former is unlikely to develop if the milk is held at 15°C. or below. Broken cream results if marked growth of B. cereus occurs. A nisin-producing strain of Str. lactis did not retard the development of the spore-former in milk, but after initial increase the numbers of B. cereus decreased. Broken cream was not prevented.

Several media previously recommended for lactobacilli by other workers have been examined, but none was found to support good growth of all species. Experiments are described in which the optimum concentrations and combinations of various ingredients, particularly Tween 80, were determined. These resulted in the development of a practical medium which has proved satisfactory for the growth of all varieties of lactobacilli.

A number of strains of streptococci falling into serological group N which could not be identified as either Streptococcus lactis or Str. cremoris were isolated during a study of the bacterial flora of raw milk (1). These organisms were dominant in milk incubated at 22°C. until the end-point of the clot-on-boiling test in three out of the twelve samples examined and, apparently, had played a major part in their spoilage. Similar strains were isolated in smaller numbers from the samples aged under other temperature conditions.

1. A diffusion cup technique using Micrococcus lysodeikticus has been found suitable for lysozyme estimation. By this method raw milk gave only small zones of inhibition. The inhibitory substance of milk was shown not to be lysozyme.

2. Dose-response curves (dilution v. pH) were obtained with Streptococcus pyogenes as the test organism. They indicated that the effect of milk on this organism was the result of the interaction of one stimulatory and at least two inhibitory substances.

3. The existence of two inhibitory substances was confirmed by dilution assays, one, L1, occurring mainly in colostrum, the other, L2, occurring mainly in milk. The inhibition is greatest when L1 and L2 act simultaneously.

4. The pH and heat stabilities of the two substances are slightly different. L1 is most stable at pH 6−6·5, 90% being destroyed at 68° C. L2 is most stable at pH 7 and 95% is destroyed at 74°C.

The apparent lytic effect of a newly formed (‘nascent’) streptococcal bacteriophage on streptococcal strains not normally lysed by the phage was shown to be actually an inhibitory action produced by high concentrations of the phage. The inhibitory effect was exhibited by stock preparations of the phage, used in sufficient concentration, and there was no need to postulate a special potency for the phage in its ‘nascent’ form. The inhibitory effect of phages on heterologous organisms was found to be a widespread phenomenon among strains of Streptococcus cremoris and Str. lactis. It became apparent only when larger proportions of phage than the traces normally used for lytic tests were employed.

1. Two spray-dried milks, one separated and one whole milk, have been stored at 25°C. for 48 and 103 weeks respectively at relative humidities ranging from 0 to 100%. At high humidities (80–100% r.h.) a rapid fall in the numbers of bacteria was followed by rapid growth of bacteria and by overgrowth by moulds. At relative humidities below 80% the number of surviving bacteria increased with decreasing humidity to maximum survival at about 10% r.h. and then tended to fall again towards 0% r.h.

2. The changes in the distribution of the different types of bacteria in the dried milks at different relative-humidities are discussed.

3. Maximum survival at 5–15% r.h. has been confirmed with pure cultures (dried in milk) of a Streptococcus and a Micrococcus originally isolated from dried milks.

4. The marked loss of viability of bacterial spores noted in dried milks stored over P2O5 or concentrated H2SO4 has been confirmed for a dried suspension of the spores of a typical strain of Bacillus subtilis.

Results of a survey of the carotene and vitamin A contents, and of the vitamin A potency, of New Zealand butterfat and butter, are presented. The butter samples were drawn from twenty representative commercial factories at fortnightly intervals over three successive years (1946–8). The survey covers the analysis of 1517 samples of fresh butter and 670 samples of stored butter.

There were uniform and regularly recurring seasonal variations in both carotene and vitamin A contents of butterfats from all North Island districts. Maximum values were found in the late-autumn/winter/early-spring, and minimum values in the late-summer/early-autumn butterfats. The seasonal trends were thus distinctly different from those which have been reported for northern hemisphere butterfats, for which the maximum values are commonly found during the summer grazing period.

The seasonal variations in carotene and vitamin A contents of South Island butterfat were less marked and less consistent than those in the corresponding values for North Island butterfat.

Variations in the unsaturated acid constituents of butterfat samples from the Manawatu district of the North Island of New Zealand over the months October to April were studied by the spectrophotometric technique, applied both before and after alkali isomerization of the fat.

The seasonal variations in the iodine values of the butterfats were found to be closely related to the changes in oleic acid content. Conjugated dienoic acids, though present in relatively small amounts, showed a somewhat similar seasonal trend in values to oleic acid. The results for percentage content of non-conjugated dienoic acids were low, and they fluctuated considerably from month to month. Conjugated trienoic and tetraenoic acids were absent or present only in traces. Small but fairly consistent quantities of nonconjugated trienoic and tetraenoic acids were found in all samples.

Large-scale manufacture of washed curd cheese has not yet been attempted in Britain. There seems to be no obvious obstacle, and the production of a good washed curd cheese would satisfy several present-day requirements. It is popular with consumers and would be an alternative to the usual standard varieties; it has certain economic advantages in manufacture and excellent properties for retail sale. In addition, low acid whey is in considerable demand as an important ingredient of certain proprietary brands of infant foods; such whey is not readily obtainable by normal cheese-making, but is produced during the manufacture of this cheese.