1. An experiment with ten dairy cows has shown that the daily feeding of 30 or 60 g. of shark-liver oil containing 80,000 i.u. of vitamin A/g. is without effect on milk yield, fat yield, the fat and solids-not-fat percentage of the milk and on the health and wellbeing of the cow.

2. The concentration of aneurin, riboflavin and vitamin C in the milk was not affected by the feeding of shark-liver oil.

3. The total carotenoids of the milk fat decreased when shark-liver oil was fed. The vitamin A content of the fat increased 1100% when 30 g. were given and 1850% when 60 g. were fed. The highest individual value reached was 390 i.u./g. fat.

The collection of samples of milk from individual quarters has usually been done either by hand milking or by sampling by hand at the commencement of milking, before the application of the teat-cups for milking by machine. The former method is laborious, and may not be entirely accurate, as it depends a great deal on constant care throughout the milking to ensure that each quarter is milked into the correct container. If the quarters are milked separately by hand, the yield of milk from the individual quarters may be affected, and if the cow is not accustomed to being milked by hand, hand milking for quarter sampling may disturb her, and affect the yield, and so the composition of the milk. Quarter sampling by hand before the commencement of machine milking does not provide a representative sample of the yield of milk from the quarter, and it does not permit a measurement of quantity of milk produced by each quarter. In connexion with some work on the composition of milk from quarters showing a positive brom-thymol blue test (Hume(i), McDowall(2, 3)) and on the influence of such milk on the quality of cheese and butter made from it (McDowall(4)); the collection of full quarter samples of milk on a considerable scale was required. For this purpose a special milking-machine claw, a milking-machine bucket, and a strip bucket were constructed. These are illustrated in Fig. 1, I–IV.

1. The sources of error and general significance of the presumptive coliform test have been studied, with special reference to manufactured dairy products.

2. Eosine methylene blue agar has been found reasonably satisfactory for isolation of cultures but unsatisfactory as a direct plating medium.

3. A wide survey of the coliform flora of raw milk and milk products has been made over a period of 11 years. The data were collected from 24,952 samples and include the incidence of presumptive positive tests at each stage of manufacturing processes, the occurrence of ‘false-positive’ tests, the detailed distribution of coliform types in individual dairy products, and some preliminary observations on ‘heat-resistant’ coliform strains.

4. Material examined included raw milk, pasteurized milk, ice cream, milk powder, condensed milk, pasteurized cream, clotted cream, butter, soft cheese, Cheddar cheese, processed cheese, swabs of dairy plant, churn rinses, and the atmosphere of dairy factories.

5. Detailed confirmatory tests were performed on 2490 presumptive positives, from which 2508 coliform cultures were isolated and classified.

6. A general ecological survey of the frequency of individual coliform types in dairying operations as a whole has been attempted.

7. Particular factors which may affect the distribution of coliform types in specific products or situations have been shown to include heat resistance, resistance to drying, chemical composition of the substrate, the effect of storage, and conditions prevailing on plant surfaces. It is suggested that the coliform flora may be partly the result of adaptation to conditions associated with each individual product.

8. The value of the presumptive coliform test has been discussed in respect of public health requirements, as a plant-control method, and in relation to economic aspects. The test is believed to be of great utility in the plant-control laboratory but of little value for public health purposes.

A cheap, easily prepared and relatively uniform agar medium, containing beef extract, lactose, peptone, yeast extract and phosphate, is described. It gives excellent results with lactic streptococci and a good growth with many other organisms.

The role of phosphate and agar in the medium and the effect of filtration is discussed. It is suggested that the value of phosphate is due partly to its buffering effect and partly to its combination with some constituent of agar to form a substance which has a growth-promoting action on the lactic acid bacteria. This active substance is largely removed from the medium if filtration through paper pulp is practised.

1. The germicidal effect of spraying hypochlorite solutions of varying strength on three different phage races of streptococci from cheese starter has been described. It has been shown that fine mists containing 0·003–0·02 p.p.m. av./cl., usually ensure satisfactory destruction of air-borne phage.

2. Below a relative humidity of about 50% hypochlorite solutions cause a slight or negligible destruction of bacteriophage particles.

3. A gelatine medium has been found useful for collecting phage particles from the air, since it could be liquefied without danger of destruction of the phage after exposure and a quantitative estimation obtained of the phage particles collected.

4. When the relative humidity was low the recovery of phage particles from the air was increased.

5. Some experiments using mists of resorcinol and propylene glycol are also reported.

As moderate dilution causes little change in the surface tension of milk, it is shown to be advantageous to use σ-dilution curves in place of the σ-values of the undiluted fluid as a characteristic of the surface properties of milk. The complications arising from the presence of the milk fat are described, and it is suggested that the influence of the fat is of a physical rather than of a chemical nature. A study of the role of the various milk proteins shows the casein to be of great importance, whilst the heat-coagulable proteins have little influence. The serum obtained after removal of the casein and heat-coagulable proteins contains a residual fraction of protein-like material which is markedly surface active though constituting only about 3% of the total milk proteins. The surface-active material (σ-proteose) has been concentrated and isolated, and its properties are described in some detail.

1. The biological value of proteins at an 8% level of protein intake measured on rats by the method of Mitchell (7, 10) was 52 for white bread of 73% extraction, 76 for Cheddar cheese, 75 for a mixture of both foods when each supplied 50% of the protein, and 67 when the two sources of protein were given on alternate days. The true digestibilities were, respectively, 99, 100, 98 and 99.

2. Similar experiments with dried skim milk and dried cooked potatoes yielded biological values of 71 for potato, 89 for milk, 86 for the mixture and 81 for the substances fed separately on alternate days. The true digestibilities were, respectively, 82, 90, 82 and 87.

3. An attempt to carry out experiments of the same type with dried whey and dried potato failed because of deaths of some rats receiving the whey diet, probably because of its high content of lactose. A biological value of 76 was obtained for the potato proteins and of 70 for a mixture of whey and potato in which whey supplied 25% of the protein. The true digestibilities were, respectively, 82 and 68.

4. The biological value and the true digestibility of the proteins of a sample of edible soya-bean flour were, respectively, 73 and 90.

5. It is concluded that there is a marked supplementary relationship between the proteins of milk and potato and those of bread and cheese when the members of each pair supply equal amounts of protein and when they are given together. No supplementary relationship is exhibited when the sources of protein are given separately on alternate days.

The ferric thiocyanate method of estimating peroxide in fats has been modified to give greater sensitivity and greater stability of the reagent. As the 96% acetone used by Chapman & McFarlane (3)and Lips et al.(4) only dissolves about 0.5% butterfat, the sensitivity of the test was increased by using, as solvent, the mixture of benzene and methanol used by Bolland et al. (6) in the determination of rubber peroxides, which dissolves at least 10% butterfat. Instead of using a prepared reagent which gradually deteriorates, the ferrous salt and thiocyanate are added in aqueous solution during the test, and, moreover, ferrous salts appear to be more stable in this solvent than in acetone. The modified method is sufficiently sensitive to measure the peroxide value of the fat of freshly drawn milk and has been applied to the study of the first stages of oxidation in milk, butter and whole-milk powder.

1. Data on milk consumption, and other relevant information, were obtained from 150, 152, 124 and 135 lower working, working, lower professional and professional class families respectively in the city of Leeds during May-June 1939.

2. An account is given of the factors affecting the consumption of liquid milk at school and at home, and of tinned milk. An estimate is made of the amount of milk consumed by children over and under 5 years of age and by adults, and of the nutritional adequacy of the milk consumption of those three groups.

3. An analysis is made of the use of milk in the home and the importance of the three factors: (a) the number of families making milk dishes, (b) the frequency with which the dishes are made, and (c) the amount used in each dish per person per time, in causing differences in the average liquid milk consumption of the four social classes.

4. An estimate is made of the extent to which families were obtaining a proper amount of milk, and the number of the families who were not spending sufficient on food to purchase an adequate amount of milk.

5. It is concluded that in investigations into the consumption of milk, the various social classes should be studied separately, otherwise fundamental differences between them fail to be disclosed.

The general experience of the retail milk trade is that considerable variations exist in the demand for milk and cream at different times of the year, and that these need careful consideration to preserve the proper balance between the supply of, and demand for milk. Different social classes of consumers are also known to exhibit different habits of milk and cream consumption. This paper examines the fluctuations of demand for milk and cream over a 1-year period of four social classes of consumers.

1. Storage tests on spray-dried full-cream milk powders prepared from milk preheated at 160,170,180, 190 and 200° F. for approximately 20 sec. and dried by the Krause process have been carried out at 47, 37 and 15° C. or room temperature. The storage tests were carried out independently at two different research stations. At the Hannah Institute the powders were packed in plain tin-plate containers as received from the factory. At Cambridge grease-free plain tin-plate and lacquered tin-plate containers were used. Deterioration was followed at both stations by a tasting panel and by determination of the amount of oxygen absorbed by the powder and of the accumulation of peroxide in the fat.

2. When fresh the powder pre-heated at 180° F. had the best flavour, followed in order of preference by those pre-heated at 190 and 200° F., which had a definite but quite pleasant ‘boiled’ or ‘cooked’ flavour, and by those pre-heated at 160 and 170° F. which had an incipient tallowy flavour, but were nevertheless still acceptable. The 200 and 190° F. powders gave a strong reaction for volatile sulphur, the 180° F. powder a much weaker but quite definite reaction, and the 170 and 160° F. powders a negative reaction. The copper content of the 180° F. powder which, with the 170° F. sample, was the highest of the group, may have been partly responsible for the weakness of the reaction for volatile sulphur given by this sample. The solubility of the 180, 190 and 200° F. powders was not adversely affected by the high pre-heating temperatures, and the moisture contents of all the powders were sufficiently low to prevent any obvious loss of solubility, which remained very good indeed throughout the storage tests.

A knowledge of the density of air-free milk solids is required for calculation of the quantity of oxygen originally enclosed in sealed cans containing milk powder, and for conversion of percentages of oxygen obtained by analysis of the headspace gas to absolute units. Determination of this figure is a matter of some difficulty owing to the presence of entrapped ‘air’ in the spray-dried product. In the liquid displacement method there is also a danger of error due to incomplete ‘wetting’ of the particles, or to solution of one or other constituent of the powder, while in the gas-displacement method error may be introduced by solution or adsorption of the gas by the powder. Lea, Moran & Smith(1) obtained values of 1·29 by a pyknometer method with ethylene glycol, and 1·31–1·32 by a nitrogen displacement method for full-cream solids containing 27% of fat. Muers & Anderson(2), on the other hand, reported values of 1·26–1·28 by a liquid-displacement method using propylalcohol. Further determinations have therefore been made by various modifications of all these methods.

1. A sample of roller-dried skim-milk powder, found to possess the very low biological value of 55.2, supplemented slightly but definitely the proteins of national wheatmeal bread when it supplied 23% of the total nitrogen. No such effect was observed with another sample of milk with a biological value of 71.1 when it supplied 17 % of the total nitrogen, or with a further sample of milk with a biological value of 81.3 when added to bread at a 6 % level supplying about 15 % of the total nitrogen. On the first two occasions the biological value for two different samples of national wheatmeal bread was 48.9 and 55.0 respectively for young rats; for the same rats when mature the values were 55.8 and 64.6. No differences attributable to age were found with milk. Baking did not affect the biological value of the proteins of the milk added to the flour.

2. The biological value of a sample of spray.dried skim milk declined from a value of 88.5, observed 18 months after manufacture, to 71.1 some 36 months later. The true digestibility remained unchanged.

3. Commercial samples of spray.dried and roller.dried skim milk of good quality, and of over.neutralized and overheated roller.dried skim milk, yielded biological values of 78.6, 80.9, 78.2 and 76.2 respectively and true digestibilities of 90.5, 90.1, 89.4 and 88.8 respectively.

1. Eighteen samples of colostrum obtained from Large White sows during parturition were examined for total solids, fat, vitamin A, vitamin B^ riboflavin and vitamin C.

2. The mean values and ranges for the total solids (fourteen samples) and fat (fifteen samples) were 23.9% (20.6–27.2%) and 3.4% (1.7–5.8%) respectively.

3. The mean vitamin A content of eighteen samples was 247 i.u./100 ml. with a range of 103.462 i.u./lOO ml., or 89 i.u./g. fat with a range of 42–137 i.u./g. fat. No β-.carotene was detected in any of the samples.

4. The mean vitamin B1 content of seventeen samples was 145 /µg./100 ml. with a range of 81.260 µg./100 ml.

5. The mean riboflavin content of sixteen samples was 45.6 µg./100 ml. with a range of 21–78 µg./100 ml.

6. The mean ascorbic acid content of seventeen samples was 23.8 mg./100ml. with a range of 12–36 mg./100 ml.