The necessity for a rapid and easy micro-method for the determination of lactose in dairy products arose during our work. The procedure for glucose determination in blood was adopted and modified for dairy products. Quantities of 1–10 mg. lactose can be estimated rapidly. Comparison with the macro-method of Lehman gave satisfactory results.

1. The body size and grading of the wastage cattle have been described. It was found that the average wastage cow is relatively small in size with an average live weight of 1100 lb. or 9¾ cwt. The condition was also disappointingly poor since over one-half of the total wastage cows are in grade C or are ungraded.

2. The seasonality of the sales shows an autumn glut, which appears to increase as the grade or condition deteriorates.

3. The annual variations in body size during the 4 years are very slight, which seems to indicate that under present circumstances the region can only maintain cows of this size.

4. It was shown that the region can be subdivided into four parts in which the average body size for each section falls into one of four well-defined ranges of weight.

The records of milk yield and infection with Streptococcus agalactiae in four herds over periods of 9–13 years were analysed, using rigorous methods of control in the comparison of yields of infected and healthy cows. Fifty-seven cows which became infected in the second to sixth lactations yielded significantly more (56·5 ± 20·4 gal./lactation; P = 0·01) before infection than did non-infected animals in corresponding periods. In thirty-two animals infected in the second to fifth lactations an average apparent loss of 194·2 ± 28·3 gal. was found for the first lactation in which infection was detected. This represents a loss of about 24 % of the lactation yield.

Individual-quarter machine milking is an important technique in the study of mastitis, dairy-cow management and milking-machine design. In the course of such work equipment for this purpose was found necessary and suitable designs had to be produced.

It is generally accepted that the udder possesses two main defence mechanisms against mastitis infections. The teat sphincter acts as a barrier against the entry of the pathogenic frequently present on the skin of the teats, and internal factors prevent the bacteria which gain access from setting up an infection. In recent years studies have been made on the relative importance of these two mechanisms, and particular attention has been paid to the relation of teat patency or ease of milking with the incidence of disease. Little (1) stressed the importance of the intact sphincter as a barrier, and suggested that the sphincters of older cows relax, making them more susceptible to infection. In an attempt to overcome the disadvantages of the manual assessment of teat patency, Espe & Cannon (2) used a special instrument. The results were not wholly satisfactory and no correlation with mastitis was found. More recently, Murphy (3) manually examined the teats of at least eighty-seven cows and found a trend towards a higher incidence of infection in quarters with patent teats. This latter author did not agree that relaxing of the teat sphincters with advance in age could account for the increased susceptibility of older cows to streptococcal mastitis (4). While Murnane (5) could not confirm Murphy's results, McEwan & Cooper (6), again using the manual method, obtained further evidence definitely suggesting that easy milking cows were more prone to mastitis. Although Stuart & Lancaster (7) found evidence confirming the importance of the teat orifice, they concluded that it was of less importance than those factors operating within the udder.

In the course of an investigation on the yield and composition of sows' milk, we have experienced difficulties in obtaining representative samples of milk for analysis.

The technique adopted was that described by Braude et al. (1) in which 5 units of pitocin were injected into the ear vein of the sow and the milk withdrawn by hand. Since the yield of these sows was being measured over a 24 hr. period each week, it was possible to compare the quantities obtained, following injection, with the average amount suckled by the litters during natural sucklings. The comparison was never particularly accurate as we found that two operators, each milking one teat, were all that could be conveniently accommodated on each side of the sow. This meant that only four glands could be milked properly. We found, too, that variations in teat size and mammary gland size affected the speed of withdrawal and the final amount obtained.

The milk from twelve individual cows in a mixed herd in Shropshire was sampled twice weekly over a period of 12 weeks, which covered the transition from winter to summer conditions of feeding. Detailed analytical results are tabulated, and certain figures presented in graphical form. In addition, bulk samples of both morning's and evening's milk were obtained and tested for fat and solids-not-fat.

On the whole the results show great individual consistency of composition, but an appreciable rise in the crude protein content of the milk from all cows took place in late April and in May, this effect being attributed to the change-over in feeding to an all-grass diet. From a consideration of the figures obtained, it is deduced that:

(1) The average composition of mid-lactation milk may differ markedly from cow to cow, but appears to be unchanged by minor alterations in the winter rations, provided these are reasonably satisfactory to begin with. There is, however, a marked increase in total protein resulting from the introduction of spring-grass feeding.

(2) The results show that a herd, although well-fed and efficiently managed, may produce milk in the late winter months, and even in the early spring, which is below the legal standard of 8·50% in s.n.f.

It has been shown that, although they are present, sulphur bacteria and streptomyces able to oxidize rubber do not affect the life of the rubber teat-cup liners of milking machines.

This paper presents in statistical form the results of the bacteriological examination of over 1200 samples of National Dried Milk during the period 1944–9. Factors which may affect the results are discussed. The general level of bacterial quality disclosed is high, but appreciable differences are shown in the standards reached at different factories and repacking depots. No general trend with time was observed in the figures throughout the period of 6 years considered, and no correlation was observed between the counts obtained and the time which had elapsed since packing into 20 oz. tins. Between counts at 37 and at 55° C. some correlation was noted in the products of most factories and depots, and the significance of this observation is discussed. The counts obtained are compared with various standards which have been put forward or are now in operation, and ways are suggested in which the figures might be used to set up standards of bacterial quality for roller-dried milk powder in this country.

Heating by means of saturated steam is used widely in the dairy industry in many processes. One application is autoclaving, a process not confined to the laboratory but used also for the preparation of sterilized milk(1). It is well recognized that the presence of air in autoclaves depresses the temperature of the heating medium when control of the process is based on measurement of pressure, but it does not appear to be generally appreciated, at least in the dairy industry, that air can depress the rate of heating of the load even when thermostatic devices are used to control the autoclave temperature. In the first place air will tend to accumulate in areas remote from the steam inlet in large vessels, with consequent reduction in partial steam pressure, and hence steam temperature, in these areas. Where the atmosphere temperature is maintained another effect occurs. This second effect is due to insulating layers of air which form on the cool surfaces of the load as the steam fraction of the mixed atmosphere condenses. A blanket of air thus formed is unable to disperse because of the general movement of the mixed atmosphere to the condensing surface.

1. The results discussed in this part of the report were obtained by examination of milk samples taken at approximately fortnightly intervals throughout a period of one year from 298 farms in eight widely separated areas of England and Wales. The samples were examined by the routine resazurin test, the methylene-blue (4½/5½ hr.) test, the methylene-blue (½ hr.) test and the temperature-compensated keeping quality test using clot-on-boiling (c.o.b.) to determine the end-point. For the first three tests, the treatment of the samples and the standards applied conformed to those prescribed officially for these tests in England and Wales. Details are given of the treatment of samples and testing procedure for the temperature-compensated c.o.b. test. With this test two standards, equivalent to a residual keeping quality at 22° C. of 21 and 24 hr. from 9 a.m. on the day of collection of the milk from the farms, for both evening and morning milk were used.

2. The results are analysed on the basis of the proportion of farms and of samples passing or failing the different tests, the effect of shade atmospheric temperature on the incidence of failures and the relationship between the standards imposed by the c.o.b. tests and the official methylene-blue (4½/5½ hr.) test.

The proportion of farms and of samples passing each test was much higher in winter than in summer and was directly related to the prevailing shade atmospheric temperature. However, a proportion of farms was consistently able to comply with the standards. No more than 5% of the total failures by any test could be ascribed to the 60 (20%) best farms, whereas the 60 (20%) worst farms were responsible for as many as 37–60% of the total failures from the 298 farms.

1. The experiments described in this part of the report were designed to obtain information about the effect of time and temperature of pre-test storage on test results and, in particular, about the possibility of a practical method of compensating test results to eliminate or minimize their dependence on the time and temperature of pre-test storage.

2. Four separate experiments were planned and carried out in three widely separated areas in England and Wales. Samples of morning milk, brought to the laboratory with the minimum of delay, were divided into a series of subsamples which were subsequently stored at controlled temperatures ranging from 3 to 24°C, and at shade atmospheric temperature, for periods ranging from 7 to 30 hr. before examination by one or more of the following tests: keeping quality at 18, 22 and 24° C. using clot-on-boiling (C.O.B.), and precipitation with 68% alcohol (A.P.T.) or 50% alcohol; methylene-blue test at 37–5° C. and at 18, 22 or 24° C. The results for the different tests were the times to end-point after transfer from the storage to the incubation baths.

A rapid method for the colorimetric analysis of micro quantities, of citric acid beginning at concentrations of 0·01% of citric acid in milk and in dairy products has been described. The analysis is based on the yellow colour which develops upon reacting citric acid with pyridine in a solution of acetic anhydride, as applied by Saffran & Denstedt for the estimation of citric acid in blood. The accuracy of the method in the ranges normally used in the estimation of citric acid in milk is approximately ±3%. Examples of determinations in milk and dairy products are given.

From raw and pasteurized milk and cheese, human, bovine and pig faeces, human nose and throat swabs, 553 pure cultures were isolated and tested by a cross-streak technique on agar. From the same sources, but without isolation and purification of the cultures, 510 samples were also tested by spotting individual colonies with a test-organism culture of Streptococcus agalactiae. A further 8016 samples were tested after enrichment by a quick assay using Str. cremoris as the test organism. The samples examined failed to reveal antibiotic producing streptococci with the exception of some strains of Str. lactis which produced nisin.

1. Thirty-five strains of acetoin producing lactic streptococci isolated from raw milk, from starter cultures and from dairy products were investigated biochemically and serologically.

2. The strains are shown to form a homogeneous unit, very similar to Strep. lactis O.J., which species they resemble in cultural behaviour, in growth-temperature range, in tolerance of sodium chloride and heat and in carbohydrate and other fermentations. They differ from Strep. lactis essentially in their ability to utilize citrate in producing CO2 volatile acids and C4-compounds (diacetyl, etc.). With few exceptions they bear no resemblance to the enterococci.

3. Serologically the strains are shown to belong to group N and thus the relationship to Strep. lactis is clearly established.

4. The strains investigated are shown to be identical with Strep. citrophilus van Beynum & Pette and almost with certainty, though no direct comparison has yet been possible, with Strep. diacetilactis Matuszewski et al. Probably they are identical, too, with Strep. diacetyl aromaticus Karnad and Strep. lactis aromaticus Joshi & Ram Ayyar.

5. The taxonomic position of the relevant unit is discussed, and it is suggested that it be given species rank under the name Strep. diacetilactis.

Twenty-three strains of lactic acid streptococci were shown to be types of Streptococcus cremoris or Str. lactis by cultural, biochemical and serological means. The antibiotics produced by the cremoris strains could be differentiated readily from the lactis antibiotics, of which at least five different varieties are described. A cross-test and a resistant-strain test were used to differentiate the antibiotics.

1. Improvements are described in the methods for the extraction and colorimetric estimation of metals in dairy produce, using the carbamate reagent for copper and thiocyanate for iron.

2. A combined filtration procedure has been developed to enable both metals to be determined on the same sample, and with slight modifications this procedure has been applied to the analysis of samples of butter, cream, buttermilk and whey.

3. The wet-ashing technique has also been improved to enable it to be used for the estimation of both metals on the same digest.

4. Comparisons show that the combined filtration method is capable of giving results which agree very well with those yielded by wet-ashing.

5. The results of many analyses show that the majority of creamery butter samples have a satisfactorily low content of both copper and iron.

6. Many whey butter samples have a rather high metallic content.

7. Notes are given on the results obtained when the methods described are applied to other dairy produce.

1. This survey was undertaken to select a test for the official examination of the keeping quality of milk, both raw and pasteurized, sampled during its distribution to the consumer. Forty-five laboratories in England and Wales collaborated in the survey and together tested 20,159 samples during the year May 1949–April 1950.

2. Failures with each test were lower in winter than in summer, and increased with increasing shade temperature. However, the proportion of failures for all samples tested in any one month at maximum shade temperatures up to 70° F., or even 75° F., was not appreciably higher than at temperatures up to 65° F. Of the samples examined during June to September, 62% were taken on days when the maximum shade temperature exceeded 65° F.

Whatever test is used for the control of milk it is reasonable to expect that at least 75% of samples taken during a given period should reach the required standard. Because of the lower incidence of failures in winter than in summer, this requirement should apply to tests done during a period of 6 months rather than one of a year.

1. The viscosity temperature coefficient of homogenized milk has been determined with an estimated accuracy of 1%.

2. The effect of temperature on the viscosity has been investigated in some greater detail.

Cheese of the Swiss (Emmenthaler, Gruyère, Danish-Swiss) type is popular on the continent of Europe and in America, but severe losses in ripening are caused by contamination with anaerobic sporeformers. Active gas production by the clostridia during ripening causes distension and spoiling of the cheese which becomes unmarketable.