1. The mean and the standard error of the mean of milk yield and of butterfat percentage have been determined for each of the first five successive Milk Recording Society tests of both afternoon and morning milk.

2. The yield of butterfat and the coefficient of correlation of milk yield and butterfat percentage at each test have been calculated.

Litmus milk is probably the most useful medium to the dairy bacteriologist, since it indicates fairly accurately what will be the action upon milk of the micro-organism under investigation. In spite of the advantages of synthetic indicators, such as brom-cresjol-purple, litmus is still used because it gives a greater variety of reactions than a synthetic indicator. Thus the reducing power of a culture is adequately indicated by litmus, the normal E being about –0·09 volt at pH 5(1). Some lactic acid bacteria, e.g. Str. lactis, readily reduce litmus, while others do not or only very slightly, e.g. Sbm. plantarum. Plain litmus milk is, however, an inadequate medium for some bacteria, which either clot the medium only after several weeks growth, or never produce sufficient acid to bring about this change (2).

It has been shown that alterations in the hydrogen-ion concentration of milk result in differences in the numbers of bacteria which survive the process of heating at 145° F. for 30 min. As the pH decreases the number of bacteria surviving also decreases. The possible bearings of these findings on various processes are discussed.

(1) 419 samples were counted in each of ten stations (laboratories) in order to assess the accuracy of the plate-count method under the conditions existing in practice.

(2) When, in each count, that plate which would ordinarily be used in practice is selected for the final count, it is found that the range which would include 95 per cent, of counts in the same sample is as wide as from one-ninth of the mean to nine times the mean when inter-station differences are taken into account. For 80 per cent, of counts in the same sample the corresponding range would be from 1/(4·1) of the mean to 4·1 times the mean.

(3) Systematic differences between stations under these conditions account for between 3 and 4 per cent, of the total experimental variation.

(4) When thirty-one complete samples in which all counts were made at a dilution of 1/10 were statistically analysed separately it was found that the range which would include 95 per cent, of counts in the same sample was from 1/(3·7) of the mean to 3·7 times the mean. For 80 per cent, of counts in the same sample the corresponding range would be from 1/(2·3) of the mean to 2·3 times the mean. There were no systematic station differences.

(5) When all plates are counted at the same dilution the error is therefore much reduced and this result suggests that the systematic station differences exhibited by the 419 samples as well as some of the random errors occurring in them is due to the combining of plate counts made at different dilutions.

In effect this means that owing to the different conditions encountered during transit comparable figures for any sample could not be expected.

In a study of coliform organisms in cream attention has been directed towards the occurrence of specific types within the group, and to their effect upon flavour and quality.

Coliform organisms were isolated from eighty-eight (or 72 per cent.) of 112 samples of cream examined. By preliminary enrichment methods 128 strains were isolated, of which ninety-eight (or 76·5 per cent.) were typical coli strains, fourteen (or 11 per cent.) aerogenes, and sixteen (or 12·5 per cent.) intermediate.

Twenty-nine coliform organisms were tested for their effect upon cream flavour and quality. The aerogenes and intermediate types were found to be similar in their effect and to produce a more rapid and serious deterioration in quality than the coli strains of faecal type.

1. Six types of surface discolorations are described and a list is given of the fungi causing these discolorations. The fungi listed are shown to be capable of reproducing the discolorations under experimental conditions.

2. The surface moulding of butter is shown to depend largely on the weather conditions at the time of removal from cold store (temperature and humidity), and the foodstuffs available from the wrapping materials.

3. The butter, boxwood and parchment are capable, in the presence of free water, of supplying substances which stimulate the germination of fungal spores.

4. The water-soluble extract of parchment stimulates fungal germination and growth. Its value as a nutrient is masked when parchment is in contact with butter. Even a well-washed parchment is capable of supporting fungal growth.

5. The butter and the boxwood are even more important as sources of soluble food material than parchment of high “water-soluble” content.

6. Glycerine is a source of food for fungi and a glycerine-softened parchment is more liable to mould attack than a glycerine-free paper.

7. It has been shown that the softening of parchment with salt does not prevent mould attack. Two strains of Cladosporium herbarum and Penicillium sp. attacked salt-softened parchment more easily than untreated parchments.

1. A description is given of internal and subsurface discolorations in unsalted and lightly salted butter.

2. Six strains of the causative organism Cladosporium herbarum are described.

3. These strains are shown to be capable of reproducing the defect under experimental conditions.

4. Four of the strains tested proved capable of slight growth at 20–24° F. (−6·6 to −4·4° C.). after 3½ months.

5. None of the strains grew at normal cold store temperatures, 15–18° F. (−9·4 to −7·7° C).

6. Salt retards the development of internal spotting. Under favourable conditions it was shown that discolorations developed in 6, 10, 16 and 25 days in butter containing 0, 5, 10 and 15 per cent, of salt in the butter serum.

1. The lactic acid flora of Cheddar cheese made from milk of certified quality form a well-defined, physiologically homogeneous group of bacteria, growing best over a temperature range of from 22 to 37° C. They may be classified into four well-defined types, Str. lactis, Str. cremoris, Sbm. plantarum and Sbm. casei, and have been studied over a period of five years. It appears from the evidence found that Str. lactis and Str. cremoris are distinct species, but that Sbm. casei and Sbm. plantarum represent different stages in the adaptation of a common progenitor to conditions in a ripening cheese. Both the streptococci and the streptobacteria appear to be unable to oxidise sugars and may thus be considered indifferent to molecular oxygen.

2. A study of their frequency distribution from the curd at making to an 18 months old cheese has shown that Str. lactis and Str. cremoris are equally viable during the first month, after which the rod forms begin to predominate, Sbm. plantarum and, later, Sbm. casei being found. The former lactobacillus is only found when the cheese is from 1 to 5 months old, the flora consisting entirely of Sbm. casei after this time. The general vigour of all strains decreases with increasing age of the cheese. There is a marked correlation between the shape of the cell, the viability of the organism in cheese and its resistance to acids and lactates.

3. The factors controlling the sequence of flora in Cheddar cheese are discussed. There is no evidence that titratable acidity, oxygen tension and differential carbon sources are responsible for the sequence. It is suggested that lactate concentration, the extent of protein degradation and osmotic pressure are factors responsible for the gradual replacement of the streptococci by the rod forms.

4. The significance of sugar fermentations by the lactic 'acid bacteria studied is discussed. The slow production of lactase is shown to be the reason for the slow growth of weakened strains in litmus milk.

5. Str. cremoris predominates over Str. lactis in the depth of the cheese in the early stages of ripening, whereas near the surface the reverse holds. Certain strains of Str. cremoris isolated from the depth of the cheese were particularly vigorous in growth in litmus milk, forming gas and beginning to peptonise the milk in about 3 days. Such strains consisted of very long chains of large cells of peculiar morphology. It is suggested that this finding is related to the known greater rate of ripening in the depth of the cheese.

Details are given of two simple tests for efficiency of pasteurisation. The first, test A, may be carried out completely within half an hour, and will detect any gross errors of pasteurisation technique. The second, test B, is more searching, and will reveal minor errors of technique as follows:

(a) 1½° F. below the minimum temperature for pasteurisation, or (b) heating (at 145° F.) for 20 instead of 30 min., or (c) admixture of 0·25 per cent, of raw milk with properly pasteurised milk. Taken together, the two tests form an efficient method for the laboratory diagnosis of faulty pasteurisation.

Attempts were made to eliminate the bacterial factor in Cheddar cheeseripening, through the agency of chloroform, and an assessment of the role of rennet was thus rendered possible.

After investigating the effect of chloroform and toluene upon the proteolytic action of rennet and trypsin in milk, the results obtained were applied in studies upon the ripening of cheese in the presence of chloroform. Cheese of normal manufacture was chloroformed at the salting stage or one week or more after manufacture (when the curd had lost its rubbery nature and the germicide was more easily incorporated). Owing to the weakened activity of enzymes in the presence of germicides, it was necessary to employ larger proportions than usual of rennet, measured additions generally being made at the time when the chloroform was added. Under these conditions the general course of protein degradation, as measured by determinations of soluble nitrogen and non-protein nitrogen, was found to be identical with that occurring in normal control cheeses. Strong evidence was thus afforded that rennet is the only important agent attacking cheese protein during the ripening process.

In the partition between the non-protein constituents of the normal and chloroformed cheeses, respectively, there were observed definite differences which tended to remain constant over the greater part of the ripening period. The relatively higher proportion of subpeptone nitrogen in the normal cheese was shown to be due, at least in some measure, to bacterial action.

Cheese ripened in the presence of chloroform developed no volatile acid, and no cheese flavour could be detected.

1. Analyses have been made of the wheys obtained at various stages in the manufacture of Cheddar cheese.

2. There is shown to be a steady rise in the concentrations of calcium and phosphorus in the wheys throughout the process up to salting. The calcium rises much more rapidly than the phosphorus.

3. After salting there is a sudden temporary fall in the concentration of both calcium and phosphorus in the whey, the calcium fall being particularly pronounced.

4. The concentration of calcium and phosphorus in the whey vary in accordance with the titratable acidity of the whey.

5. In normal cheese making some 60 per cent, of the calcium and 57 per cent, of the phosphorus in the milk is retained in the cheese.

6. Of the minerals lost in the whey some 86 per cent, of the calcium and 90 per cent, of the phosphorus escape before running.

7. An increase in the acidity of the milk before renneting increases the loss of minerals in the whey and reduces the calcium content of the cheese.

1. The buffer values of wheys obtained at various stages of the cheesemaking process have been determined over the pH range 3·5—7·5.

2. The buffering between pH 3 and 5 is shown to be chiefly due to lactate, while that at higher PH values is chiefly due to calcium phosphate.

3. The results of the buffer determinations are shown to be in accord with the analyses of the mineral constituents of wheys reported in the first paper of this series (1).

1. Determinations of acidity, lactose and lactic acid were made at various stages during the souring of milk by starter cultures, both with and without the addition of a neutralising agent.

2. Throughout the fermentation, the increase in acidity of the milk was accounted for quantitatively by the amount of lactic acid produced.

3. In some instances in the early stages of the fermentation a considerable quantity of the lactose appeared to be converted to substances other than lactic acid.

4. Over the whole fermentation the amount of by-products produced from the lactose was small.