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.

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.

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.

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. 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.

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. Four experiments with 108 rats to compare the nutritive value of sow's milk and cow's milk are described. In Exps. 1–3 the milks were fed on a comparable basis of caloric value.

2. In the first experiment, in which the milk intake was equalized, rats receiving diluted sow's milk grew at a significantly faster rate and utilized their calorie intake more efficiently than rats receiving cow's milk.

3. In the second experiment, again with equalized milk intake, rats receiving sow's milk utilized their calorie intake significantly more efficiently than rats receiving diluted evaporated cow's milk.

4. In the third experiment in which the milks were given without stint, rats receiving diluted sow's milk either with or without the addition of a synthetic vitamin supplement, grew at a faster rate, and utilized their calorie intake significantly more efficiently than rats receiving cow's milk either with or without the same vitamin supplement. The vitamin supplement did not improve the nutritive value of either milk.

5. In the fourth experiment the biological value of the proteins in freeze-dried sow's milk (85·1) proved significantly lower than in freeze-dried cow's milk (90·1).

1. The reworking of stored butter stimulates dormant bacteria into renewed growth and, since these are frequently taint-producing organisms, may hasten the deterioration of retail butter.

2. Blends of sweet cream and ripened cream (acid) butters may contain a greater variety of organisms than reworked samples of either type, and conditions may be created which are even more favourable for bacterial activity.

The changes in the volatile acidity and other factors during the ripening process of Stilton cheese have been studied. The growth of the mould was characterized by an increase in the fat-soluble fatty acids derived from the cheese fat.

Pricking the cheese ensured a more uniform blueing and hastened the ripening. There was no evidence that judicious pricking at 2 months after manufacture seriously affected the course of the ripening. Excessive pricking, however, produced abnormal cheese of poor keeping quality.

The loss of calcium and phosphorus during the manufacture of hard pressed (Cheddar) and impressed (Stilton) cheese made from the same bulk of milk has been studied. It is found that there is little loss of mineral salts from the hard pressed variety either after cutting the curd during making, or while the cheese is ripening. In the case of the unpressed variety there is constantly increasing percentage loss of minerals, correlated with an increase of titratable acidity in the whey, until the last stages of manufacture when the cheese are removed from the hoops for scraping.

The figures confirm those previously found (i) that in the cheese examined 57–58% of the calcium and 50–51% of the phosphorus present in the milk originally used, remains in the hard pressed ripe cheese, but that only 6–8 % of the calcium and 27 % of the phosphorus are left in the unpressed variety when ripe.