1. Data from seven winter feeding experiments with dairy cows, using 3×3 latinsquare designs and from two randomized block experiments on the supplementation of summer grazing, were used in a study of some aspects of experimental technique.

2. In the 3×3 trials the use of observations from 2 weeks instead of the last week of each period reduced minimum significant differences by 0·1 lb. milk/cow/day, and 0·06 and 0·02 mean percentage unit of fat and solids-not-fat, respectively.

3. In three out of four experiments no advantage was obtained from recording live weights on more than 1 day at the end of each period.

4. It was shown that the analysis of variance of milk yields expressed as individual differences between yield in the experimental period, and the mean of pre- and post- experimental control periods was considerably more efficient than that of yields in the experimental period, or covariance with yield in the initial control period.

5. The results were discussed in relation to the sources of error involved, and the relative efficiency of various types of experimental design.

1. Four hundred and sixteen individual cow samples of milk from fourteen herds were analysed for fat, total solids, crude protein, lactose and chloride.

2. Wherever possible information concerning feeding, incidence of mastitis, age of cow, stage of lactation and successful service dates was collected.

3. The milk samples were divided into normal (with 8·50% S.N.F. or over) and substandard (with less than 8·50% S.N.F.) groups.

4. The difference in S.N.F. content between the normal and substandard groups was due almost equally to a drop in lactose and protein, but with the latter playing the major part. Thus, although inadequate feeding was probably a major factor in lowering the S.N.F. in this population the fact that the lactose content was so often low was taken as indicating that mastitis was also important.

5. Breed, age of cow and stage of lactation all affected the incidence of low S.N.F. milks.

6. On average the substandard milks showed a reduced fat content as well as a lowered S.N.F. level.

The shape of the lactation curve in guinea-pigs has been studied. The peak was found to occur between days 2 and 3.

The oxygen consumption and lactose synthesis rates were investigated in mammary gland slices and results expressed on both DNA and DW bases.

Oxygen consumption rates on a DNA basis tended to be low at the onset of lactation and high at the peak. Lactose synthesis on a DW basis tended to decline linearly from the onset of lactation, but on a DNA basis showed a peak coinciding with that of the lactation curve.

The significance of these findings has been discussed.

The initial rate of growth of Str. lactis and Str. cremoris in skim-milk depends upon the proportion of CO2 present in solution. When CO2 is constantly swept from the milk medium by a stream of CO2-free gas all strains show a very prolonged lag period. They eventually emerge from this lag period after more than 8 hr. and grow well enough to coagulate the milk within 24 hr. For optimal initial growth the lactic streptococci require the presence in solution in the milk of proportions of CO2 within the range 0·2 and 2·3% by volume. Some strains have a higher CO2 requirement within this range than others. Skim-milk after sterilization contains less than the optimum proportion of CO2 for many strains of lactic streptococci.

Yeast extract in a proportion of about 0·5% can substitute for CO2 in skim-milk.

The periodic inversion of cultures in plain skim-milk reduces the initial rate of growth of some of the streptococci, particularly those which form long chains. The reason for this is unknown. It does not occur when yeast extract is present.

The determination of apparent lactic acid has been used as a basis for a rejection test for raw milk. The method consists of precipitation of milk proteins with barium chloride, sodium hydroxide and zinc sulphate, and the addition of ferric chloride to the filtrate to produce the yellow colour of ferric lactate. Lactic acid is not solely responsible for the production of the yellow colour, which, nevertheless, gives a good relationship with keeping quality of milk (measured as hours to the C.O.B. end-point at 22° C.) and the values have been expressed as ‘apparent lactic acid’.

The relationship of winter and summer milks to keeping quality has been studied, and a value of 0·03% apparent lactic acid in milk is equivalent to an average keeping quality of 5¾ and 8½ hr. for winter and summer milks, respectively. A value of 0·03% is recommended as the earliest value of apparent lactic acid at which milk could be rejected.

The apparent lactic acid in colostrum and late-lactation milk and in milk from cows suffering from mastitis has been determined, and only in late-lactation milk were the values found to be significantly higher than usual in fresh raw milk, and an inverse relationship between yield and apparent lactic acid is suggested.

Permanent glass matching disks have been prepared for use in a Lovibond comparator. This permits the intensity of the yellow colour produced with 1% ferric chloride to be determined and the apparent lactic acid in milk estimated.

Grateful acknowledgement is made to the management and staff of the Dairy Department of the Reading Co-operative Society and the Farmer's Clean Milk Dairy, Reading, and local milk producers for supplying samples for experiments; to the N.M.T.S. staff in Reading for help in finding suitable farmers, and to the Dairy Husbandry Department of the N.I.R.D. for information about and samples of abnormal and late-lactation milk. Our particular thanks are due Miss Marie Gruber for technical assistance, to Dr N. J. Berridge for the suggestion and help on the work on pH change as an indication of keeping quality (given in the appendix), and to Dr A. T. R. Mattick for the advice given in this work.

Tests over a 2-year period of milk from an Ayrshire herd showed that there was a greater incidence of low S.N.F. samples from milk with a high cell count compared with samples from that of a low cell count.

While a wide variation in S.N.F. was found at any particular cell count level, there was a broad correlation between cell count and S.N.F., the average S.N.F. for cows in the same lactation being lower for those animals with high cell counts in the milk.

It is suggested that a cell count > 100,000/ml. in bulk milk should be regarded as significant.

Bacteriological examination of the high cell count samples showed that in a large proportion of cases no typical mastitis-producing organism could be isolated.

The authors wish to thank their colleagues in the Bacteriology, Chemistry and Veterinary Investigation Departments for assistance in this work.

1. The phospholipids of skim-milk, buttermilk and butter prepared from one bulk of Friesian milk were examined, using chromatographic methods. No major differences were found between the three products.

2. The phospholipids of buttermilk contained (in moles %) phosphatidylethanolamine 29, phosphatidylserine 10, phosphatidylcholine 33, sphingomyelin 19. The content of lipid-bound inositol was 5 moles % and of plasmalogens 3 moles %. Nitrogen, associated with the kephalin fraction, equivalent to 14 moles % of the lipid P was not identified. No lysoglycerophospholipids were present.

3. Unsaturated fatty acids were present in both the α'- and β-positions of the milk glycerophospholipids, in contrast to those from other animal sources which have usually been found to contain unsaturated acids in the α'-position and predominantly saturated acids in the β-position.

The authors are indebted to Prof. H. D. Kay for providing facilities at the National Institute for Research in Dairying, Reading; to Dr R. H. Smith for advice on processing, and to Miss H. R. Chapman and the staff of the Experimental Dairy for carrying out the dairy work.

This work forms part of the programme of the Food Investigation Organization of the Department of Scientific and Industrial Research. Mr P. Whiteley contributed to the experimental work.

1. The composition of the milk of six low-plane and six high-plane ewes has been studied. Definite lactational trends have been observed for all the major constituents.

2. For all the ewes the initial colostrum was characterized by very high protein and fat contents and by low lactose content.

3. Analyses of the mineral constituents—calcium, magnesium, sodium, potassium, phosphorus, and chloride—are reported covering the whole lactation of twelve sheep. The colostrum of the low-plane animals was higher in total mineral content than that of the high-plane animals.

The author wishes to thank Mr L. J. Lambourne for providing the milk samples and Mr J. E. Allen for the spectographic analyses.

The purpose of any pasteurizing or sterilizing plant is to bring about the heat inactivation of bacteria or bacterial spores. It is generally considered for convenience that the bactericidal effect takes place almost entirely in a holding period, during which the milk can be considered to be held at a fixed temperature for a minimum time. In practice, since the milk cannot be instantaneously heated and cooled, there is a progressively increasing lethal effect throughout the period when the milk is approaching its holding temperature, and a decreasing effect in the cooling period. There is, therefore, a considerable lethal effect above that due to the nominal holding time. This has been shown in a paper by Ball(1) in which methods of calculation developed for the canning industry are applied to the problem of high-temperature, short-time pasteurization of milk. The higher the final milk temperature, the greater will be the proportion of lethal effect due to the come-up time, until, at temperatures of the order of 135° C., the lethal effect during holding may be relatively slight.

1. Four batches of soft cheese were made using rennet coagulation from both raw and pasteurized separated milk standardized to contain 1·5% fat and 7% added sodium chloride.

2. The yield of pasteurized milk cheese was about 3·33% higher than that of raw milk cheese.

3. Pasteurization of the milk improved the flavour and the texture of the fresh cheese, but had no marked effects on the body and general appearance.

4. The shelf keeping property after 4–5 days under the conditions of these experiments was better for the cheese made from raw milk. Reasons for this apparent anomaly are discussed.

5. Chemical analyses showed a greater moisture retention by the pasteurized milk cheese, leading to a lower content of fat and total nitrogen but increased sodium chloride in solution. Some retention of heat coagulable protein in the pasteurized milk cheese was suggested by a higher total nitrogen in dry-matter figure and by a lower nitrogen content of the pasteurized milk whey.

6. Pasteurization of the milk greatly reduced the total bacterial population of the fresh cheese and also the acidity of the whey produced.

A comparison of three different media, yeast dextrose agar, tomato dextrose agar and acetate agar (which is selective for lactobacilli) showed that the acetate medium was satisfactory for the isolation and counting of lactobacilli from Cheddar cheese during ripening. Lactobacilli were isolated on this medium in the early stages of ripening when the large numbers of starter streptococci growing on the other media were completely suppressed. Lactobacilli isolated were identified biochemically and serologically. Serological typing was found to be a useful method of identifying large numbers of isolates and of assessing the incidence and distribution of particular types in the cheese.

We wish to thank Dr A. T. R. Mattick for his interest and helpful advice in this work; Dr L. A. Mabbitt for preparation of the cheese samples; Miss H. R. Chapman for making the experimental cheese; and Mrs P. Jarrett for technical assistance.

1. Certain starter cultures have been found to be inhibited in the presence of milk peroxidase.

2. A high correlation has been established between the inactivation of milk peroxidase and of the inhibitory action by use of critical values of any of the following: temperature, pH, concentration of either sodium azide or hydrogen peroxide.

3. The inhibitory action can be overcome by the addition of certain reducing substances such as cysteine and sodium hydrosulphite.

4. The inhibitory action is exhibited by the corresponding separated milk and whey.

5. It is suggested that this inhibition may be due to the formation of a specific inhibitory oxidation product having a quinonoid structure.

6. The addition of 1–2% of pasteurized milk or whey to autoclaved milk caused total inhibition, whereas such additions to milk heated to 190° F. showed no such effect. This is attributed to the presence of SH groups in the latter milk capable of reducing the oxidation product.

7. It is suggested that the inhibition due to peroxidase is identical with that ascribed to lactenin 2, and that the inhibition described in our previous paper as due to ‘agglutinin’ is identical with that ascribed to lactenin 1.

1. Thirty-six 9–11-week-old Large White pigs in nine blocks of four litter-mates were individually fed on diets containing either white fish-meal or various amounts of dried skim-milk as the protein supplement. The pigs were fed according to live weight and a scale up to a maximum of 6½ 1b. of meal/pig/day.

2. There were no significant differences in rate of growth or efficiency of food utilization between pigs given the diets containing as protein supplements either 10% white fish-meal reduced to 7% at 130 1b. live weight, 10% dried skim-milk reduced to 7%, or 15% dried skim-milk reduced to 10½%.

There was, however, a trend towards an improvement in both rate of growth and efficiency of food utilization with increasing levels of skim-milk in the ration, and the differences between the high skim-milk diet (20 reduced to 14%) and the low (10 reduced to 7%), and also between the former and the fish-meal diet, reached statistical significance.

3. The difficulties of drawing any definite conclusions from the results about the relative value of the protein in white fish-meal and dried skim-milk were discussed in relation to (a) the probability that the white fish-meal diet used contained over-generous supplies of protein, and (b) the higher energy value of dried skim-milk as compared with white fish-meal.

4. The commercial grading of pigs on all four treatments was very good. The carcass measurement data indicated a tendency for the skim-milk diets, particularly those containing either 10 or 15%, to result in some increase in both back fat and belly thickness. The possibility that this was associated with the higher energy/protein ratios in the skim-milk as compared with the white fish-meal diets was discussed.