An improved method for the determination of fat-globule size distribution has been worked out and applied to samples of sow's milk drawn sequentially. The distribution patterns for the globule sizes of sow's milk have been determined. Globules range in size from less than ½μ to over 7μ. The maximum number of globules occurs at different sizes in different sows, the largest maximum size group so far recorded being 2–2·5μ, the smallest maximum group being 0–0·5μ. There is no marked trend in size with stage of milking, though usually the maximum size is less for later milkings if it changes.

The strippings of sow's milk, unlike those of the cow, do not appear to be richer in fat than the earlier milk. Also unlike the cow, the globules of sow's milk do not cluster or clump (see Fig. 1). This explains the slow rate of creaming of sow's milk.

1. A record has been made of the volume of the trade in surplus calves in Great Britain for the period 1940–50; it has averaged one and a quarter million calves each year. The highest numbers sold in any year occurred in 1946 (Fig. 1).

2. The seasonality of calf sales showing an annual increasing volume of autumn calves (with October the peak month) is a reflexion of the development of dairying and of the priority for winter milk (Fig. 2A and Fig. 3, Sheets 1 and 2).

3. Of the total calves 46.7% were classified as bobbies and 50.8% as veals. The small remainder consisted of stirkies (other strong calves), casualties and those unfit for human consumption (Table 1).

4. Nearly 63% of the veals were 3rd quality and only about 12% of the 1st quality.

5. The seasonality of veal deliveries showed a maximum proportion in June (with a correspondingly lower proportion of bobbies in that month). The maximum numbers however correspond with the maximum gross deliveries in October (Fig. 2B).

6. There has been an annual deterioration in the quality of the surplus calves as indicated by: (a) the lower proportions of veals in the total during each year, (b) the higher proportions of 3rd quality veals in the total veals each year, and (c) the reduction in the monthly proportions of 1st quality veals.

7. An attempt has been made to relate the calf sales to calf births and populations of under 1-year-old cattle and of total cows.

8. It is estimated that the calf crop as a percentage of the total cows has improved since 1940, and for the last 8 years it has averaged 92%.

1. A study of the ability of pure cultures to reduce methylene blue and resazurin at 37·5° C., to reduce methylene blue at 22° C. and to cause milk spoilage as measured by precipitation with 68 % alcohol, and the clot-on-boiling test has revealed marked differences in behaviour between cultures.

2. At 37·5° C., with the exception of two cultures, there was good agreement between the time of reduction of methylene blue and resazurin. The two exceptions were a group B Streptococcus which reduced methylene blue but failed to reduce resazurin during the 9 hr. period of observation and an unclassified Streptococcus growing at 45° C. which reduced resazurin before methylene blue; the latter dye was found to retard the multiplication of the culture slightly.

Bacterial phosphatases of growing organisms can be simply demonstrated by incorporating di–sodium–p–nitrophenylphosphate (pNPP) into suitable media. The phosphatase content of a bacterial suspension can be assessed by incubating a measured amount of it with unbuffered or suitably buffered pNPP solutions. The yellow colour (in alkaline solution) of p-nitrophenol liberated from the substrate by phosphatase can be measured accurately and conveniently in a photoelectric absorptiometer, or estimated in a Lovibond comparator using permanent colour standards. The usefulness of the tests for differentiating between members of certain genera is demonstrated by the reactions of Bact. aerogenes and Bact. cloacae, for which a close relationship between phosphatase production and gelatine liquefaction times has been found. The optimal conditions for hydrolysis of pNPP by the phosphatase of a strain of Bact. aerogenes have been established.

1. The present work was planned to provide an explanation of the lack of correlation for individual samples between the results of dye-reduction tests at 37·5° C. and keeping-quality tests at 22° C. A special study was made of the particular part played by the staphylococci (in thirty-eight samples) and the coli-aerogenes group (in thirty-seven samples) in dye reduction at 37·5° C. and in keeping quality at 22° C. A detailed study was also made of the changes in bacterial flora of twelve samples during incubation at these temperatures.

2. In milk, after overnight storage at 14° C., staphylococci were found to constitute only a small proportion of the bacterial flora, but their numbers increased during incubation at 37·5° C. (for the dye-reduction test) and at 22° C. (for the clot-on-boiling test). At the time of dye reduction staphylococci were found to constitute a major part of the bacterial flora, particularly in samples taking 5 hr. or more to reduce the dye. Although the staphylococci increased in numbers during incubation at 22° C. they constituted only a relatively small proportion of the flora at the time of the end-point of the clot-on-boiling test.

3. Initially the coli-aerogenes group were found to constitute only a small proportion of the total bacterial flora. Some growth usually occurred during incubation at 37·5 and 22° C.

The difficulty of keeping herds free from Strep. agalactiae for long periods has been demonstrated in five herds. In one sense, however, these herds were not representative of the majority of herds for they were relatively large and under the same management. Furthermore, if one herd became infected with the streptococcus, there was a real risk of the infection spreading to all herds via the hands of the relief milker, particularly if hand stripping was practised and no special precautions were taken by the relief milker.

There is no doubt that herds under the same management should take stringent precautions against the spread of infection between herds.

The corynebacteria that were isolated by non-selective methods from raw and pasteurized milk are of two main types: (1) heat-sensitive diphtheroid organisms which appear to be derived principally from the animal body, and (2) thermoduric saprophytes originating from dairy equipment. The characters of group (2), which are discussed in detail, indicate that all the cultures examined belong to a single species, Corynebacterium lacticum. Reasons are given for classifying that species in Corynebacterium and for suppressing the genus Microbacterium.

The presence of fat in milking machine liners is probably the chief cause of their deterioration. The primary effect of the fat is to cause softening and swelling of the rubber and greasiness of its surface; the secondary effect is to increase greatly the rate of oxidation. The primary effect may be reversed by removing the fat by solvent extraction or prolonged treatment with cold caustic soda; the secondary effect is irreversible.

Although the fat is derived chiefly from milk, rubber absorbs fat only slowly from liquid milk. Thus it is likely that most of the absorption is from milk residues remaining on liners between milkings, under conditions which favour the breaking of the natural emulsion. Such conditions would include drying, souring or other bacterial activity, and the presence of traces of detergents which act as protein denaturing agents.

Thus, if the widely recommended technique of cold or tepid rinsing is properly practised (8), fat absorption is kept to a minimum, and the life of liners will be prolonged. Under such conditions the absorption of fat from the cow's skin will be more important and methods of removal, or of prevention, such as the use of fat-resistant rubber may be advantageous.

Of thirty-five strains of streptococci isolated from milk produced in the Jura mountains, two were strains of Streptococcus cremoris. It appears, therefore, that this organism occurs in the wild state.

Although milk may be considered to be the normal habitat of the lactic streptococci, their adaptation to this environment must have followed the domestication of mammals, for these organisms are not pathogenic and do not normally occur in the udder. If this reasoning is accepted, then the small biological age of these organisms logically follows, and possibly they are the youngest members of this genus.

1. Twelve Shorthorn cows were used for an investigation into the effect of diets low in roughage and high in concentrates on the fat content of milk.

2. An experiment was conducted with initial and final control periods. During the control periods all the cows received daily 17 to 21 lb. of hay, 30 lb. of mangolds and 4 lb. of a balanced concentrate mixture per 10 lb. of milk. In the period of experimental treatment, lasting 4 weeks, a control group of four cows remained on this diet. Two other similar groups received daily only 6 and 2 lb. of hay, but this was supplemented with 9 lb. of a concentrate mixture low in fibre and protein. The same allowances of mangolds and of concentrates for production were given to these as to the control group.

3. The mean fat content of milk produced in the last 2 weeks of the period of experimental treatment by cows receiving the diets low in roughage was 0·49 % (group receiving 6 lb. of hay) and 0·59% (group receiving 2 lb. of hay) below that produced by the cows receiving the control diet, these differences being statistically significant. In the group receiving daily 6 lb. of hay the drop in fat content was accompanied by an increase in the yield of milk and there was only a small fall in the yield of milk fat, but in the group receiving daily 2 lb. of hay there was a significant fall in the yield of fat. The latter fall represented a loss of 18·9% of the fat as compared with the control group. The fat content of the milk and the yield of milk rapidly returned to normal when the cows reverted to 18 lb. of hay per day.

4. The butterfat produced by the cows receiving diets low in roughage had a higher iodine value and lower softening point than that from the control cows. The fat from the group receiving daily 2 lb. of hay, but not that from the group receiving 6 lb. of hay, had a distinctly lower Reichert value than fat from the control group. The treatments caused no change in the saponification value.

5. The level of solids-not-fat in the milk was not affected by reduction in the roughage intake.

1. Attempts to produce in rabbits group N sera for Streptococcus cremoris, using suspensions of living, disintegrated and heat-treated bacterial cells, yielded only non-specific products, cross-reactions occurring most commonly and intensively with HCl extracts of the streptococci of groups K and L.

2. The non-specific antibodies in these sera were completely removed by absorption with streptococci of group K or L, the group N reactions being only partially impaired.

3. In order to inactivate, before immunizing rabbits, that antigen in the ‘cremoris’ cells responsible for stimulating the production of non-specific antibodies, the organisms were ‘absorbed’ with an excess of group K or L antiserum.

4. With suspensions of organisms treated in this way, potent group N specific precipitating sera were obtained for both freshly isolated and freeze-dried strains of Str. cremoris.

5. The identity of Str. cremoris with serological group N is thus established.

Using non-selective methods of isolation, the species that was detected with greatest frequency in raw milks of varying purity is Alcaligenes viscosus. The majority of the cultures do not produce a ropy condition in milk or other media. In some strains the oxidation of citrate, and hence the production of alkalinity in milk, is slow and erratic, being dependent on the occurrence of a mutation. The only Gram-negative rod detected in laboratory-pasteurized milk was A. tolerans n.sp., a description of which is given. That species is similar in general character to A. viscosus but differs principally in its greater resistance to heat, its inability to attack fats, and its erratic and usually poor growth on laboratory media. Greatly improved growth on nutrient agar is obtained by the addition of lactate and relatively high concentrations of ferrous or ferric salts.

Of 161 cultures of aerobic sporeformers isolated from raw and pasteurized milk 96 were found to be B. cereus, 27 B. mycoides, 17 B. subtilis, 11 B. sphaericus, 3 B. megatherium, 2 B. pumilus, 1 B. firmus and 4 were unidentified strains.

Typical broken cream followed by rapid sweet curdling of sterile milk was produced by 36 of 39 strains of B. cereus and 5 strains of B. mycoides examined. Three strains of B. cereus failed to produce broken cream. These 3 strains were atypical in that they failed to produce lecithinase, unlike the remaining 93 strains isolated during this study. Other species of aerobic sporing bacilli tested, including 17 strains of B. subtilis, 10 of B. sphaericus, 2 of B. megatherium, 2 of B. pumilus and 1 of B. firmus, all failed to produce broken cream and in fact produced no visual change in milk within 48 hr. at 22° C.

Under the conditions of our experiments, 48 out of 60 samples of fresh farm milk and 12 out of 14 samples of freshly bottled pasteurized milk developed broken cream within 18 hr. at 22° C. followed by sweet curdling within a further 24 hr. Strains of B. cereus or B. mycoides were isolated from all samples showing broken cream, but only 3 atypical strains of B. cereus were isolated from the 14 samples which did not develop the fault.

It seems that the production of broken cream is in some way associated with the production of lecithinase by B. cereus and B. mycoides. This view is supported by the fact that three non-lecithinase producing strains of B. cereus were also unable to produce broken cream. However, attempts to reproduce the fault by adding a concentrated culture filtrate to sterile milk or cream were unsuccessful.

Because of the widespread distribution of spores of B. cereus and B. mycoides in both raw and pasteurized milk, the absolute prevention of broken cream does not seem possible, but preliminary observations suggest that maintenance of milk at 5° C. or lower from the time of pasteurization until delivery to the consumer may sufficiently delay the onset of the fault to obviate the difficulty in practice except in very hot weather in households where insufficient care is taken to keep milk cool.

Streptococcus diacetilactis, isolated from spontaneously soured potato mash, was first described by Matuszewski, Pijanowski and Supińska in 1936(3). Its essential features included the production of large amounts of lactic acid and volatile products (including diacetyl), and it differed from the ‘lactis-cremoris’ group primarily in the production of carbon dioxide in milk, the utilization of citrate and in its vegetable origin. More recently, in his investigation of certain diacetyl-producing and citric acid-fermenting streptococci from milk and from starter cultures, Swartling(5) showed that strains which resembled closely the Str. diacetilactis of Matuszewski et al. belonged to serological group N. In an addendum to his paper, Swartling states that this observation has been confirmed by me with a freshly isolated strain of Str. diacetilactis (no. 2) received from Prof. Pijanowski and Dr Supińska the purpose of this Note is to record the experimental evidence for that statement.

During the twelve years from 1935 to 1946 the type of foods given to sixty-one Dairy Shorthorn first calvers during the months of February and March changed so that the dry-matter intake of the cows rose and the dietary fat fell, but there was little change in the Protein and Starch equivalent they received.

Milk yield varied directly with the amount of fat and starch equivalent in the diet and inversely with the dry matter.

The solids-not-fat percentage of milk varied directly with the amount of starch equivalent, and inversely with the dry matter content, of the diet.

The milk-fat percentage was not influenced by the foods given.

It was shown that the fall in the level of solids-not-fat in the milk was largely due to the increase in the dry matter intake of the cows.

The keeping quality of various mixtures, made up of raw milk and skim milk-powder in varying proportions, has been studied. It has been found that the keeping quality of unpasteurized samples containing milk powder was slightly better than that of raw milk. The keeping quality of the pasteurized mixtures was satisfactory during the time of storage for 40 hr. at 23 and 18° C. and for 60 hr. at 10° C.

Three strains of B. cereus were grown in milk at nine different temperature combinations. Broken cream could be prevented by holding milk at 5° C. or lower for 24 hr. before transferring to 15 or 18° C. for a further 24 hr., but with a subsequent period of storage at 22° C. the fault was not prevented. Broken cream developed after storage at 10° C. followed by 18 and 22° C., but not in milk kept at 10° C. and then transferred to 15° C. After preliminary storage at 15° C. the fault appeared within a further 24 hr. regardless of the subsequent storage temperature.

With two strains of B. cereus it was observed that pasteurization accelerated spore germination and hence the development of the fault. With low levels of inoculum there was delay in the appearance of the fault with one strain of the organism.

In twenty-four samples of commerically pasteurized milk it was shown that the fault could be controlled by refrigeration at 5° C. before distribution except when the subsequent temperature was allowed to rise to 22° C.

Contrary to the suggestion made by Davis (15) preliminary observations indicate that the growth of B. cereus and the development of broken cream is not inhibited by the presence of acid-producing organisms such as Str. lactis.

1. The failure of clostridia to produce a butyric acid fermentation, when known to be present in Swiss-type cheese, is discussed.

2. It is suggested that inhibitory substances produced by the predominating lactic flora of young cheese are partly responsible for the suppression of the fermentation.

3. Details are given of the techniques used to investigate this supposition.

4. The evidence was obtained by examining fifty-one samples of Gruyère cheese, 78% of which were contaminated with clostridia. 85% of the samples contained inhibitory lactobacilli.

5. In 30% of the samples the inhibitory phenomena were sufficiently marked to give clear zones of inhibition against Staphylococcus aureus when a suspension of cheese was placed in penicillin cups.

6. Inhibition of Clostridium butyricum was demonstrated with pure cultures of lactobacilli. The cultures could grow at temperatures from 30 to 50° C, but were inhibitory only at certain temperatures of incubation which appear to be a strain characteristic.

7. The inhibitory substance(s) concerned is not nisin because it is acid and heat labile.

1. The results of experiments on the changes with temperature in the relative viscosity and viscosity of whole milk have been considered.

2. Some inconsistencies have been traced and amendments proposed.

3. It has been suggested that values for the relative viscosity and viscosity of whole milk cannot usefully be regarded as independent of the experimental circumstances in which the observations were obtained.

4. Empirical curves have been calculated for the viscosity-temperature relations, in forms convenient for practical use in circumstances similar to those of the experiments examined.