1. Fifteen samples of raw and fifteen samples of commercially sterilized milk from the same bulk were analysed for vitamin C by the chemical method (titration with dichlorophenol-indophenol).

2. The raw milk contained on an average 1·83 mg./100 ml. of total (reduced and reversibly oxidized) ascorbic acid. The corresponding figure for sterilized milk was 1·03 mg./100 ml., a loss of 43% of the original value.

3. Storage of the sterilized milk for a period of 4·6 weeks resulted in a further reduction equivalent to about 30%.

The N distribution in terms of casein, albumin, globulin, proteose-peptone, and non-protein N is given for a number of samples of normal milk, of milk from cows with mastitis, and of milk persistently low in solids-not-fat content. Improved methods of determination have been used.

The average N distribution in normal milk is as follows: casein N 78·5, albumin N 9·2, globulin N 3·3, proteose-peptone N 4·0 and non-protein N 5·0% of the total N. The casein N figure is the least variable, ranging from 77·3 to 80·7. On this basis, normal milk contains, as an average: casein 2·63, albumin 0·31, globulin 0·11, and proteose-peptone substances 0·13%. The total protein content is 3·18%, and the casein: albumin: proteose-peptone: globulin ratios are 23·8: 2·8: 1·2: 1·0.

The milk from cows with clinical mastitis is low in solids-not-fat content, and characterized by a decreased content of casein and an increased content of albumin, globulin, and proteose-peptone substances, particularly of globulin.

The milk samples of low solids-not-fat content were of normal appearance and reaction, and produced by apparently healthy cows known to have yielded milk of low solids-not-fat content for some time. The samples were examined by strict bacteriological methods for the presence of mastitis streptococci, and formed two distinct groups: (1) samples from cows with subclinical mastitis, having the protein distribution of the mastitis samples described above, the cause of the low solids-not-fat being pathological; and (2) samples from uninfected cows, having the protein distribution of normal milk, the cause of the low solids-not-fat being physiological. The two groups of low solids-not-fat cases are discussed, and the conclusion drawn that subclinical mastitis may account for a large proportion of these widespread and puzzling cases.

Many cases of mild subclinical mastitis cannot be detected by the simple chemical tests which will reveal pronounced infection, and satisfactory bacteriological tests, when available, demand much skill and time. For the detection of milk from cows with subclinical mastitis, and for the differentiation of milk samples with pathological and physiological low solids-not-fat, the solids-not-fat, the figure is suggested, and the advantage of this “casein number” is illustrated.

Rinds from home-produced and Dominion Cheddar cheese contain from 15 to 20 % of moisture, but those from unripe cheese contain up to 27 %. Salt tends to diffuse into the interior of cheese while the rind is slowly drying, but the rate of diffusion is not quantitatively proportional to the moisture content, although closely approached in cheese requiring a long period of ripening.

There is an appreciable loss of fat from the rind through absorption by the bandage. The fat has a high acid value and carries the characteristic taste of the rind.

Rinds have a higher crude protein content than the interior of cheese; the extent of protein breakdown is less but can be correlated with that in the interior of the cheese.

Rinds contain higher calcium and phosphorus contents in the dry matter and a higher Ca/P ratio than the interior of cheese.

The fibre content of rinds is negligible. The content can be gauged from a visual inspection of a sample for portions of bandage.

1. The effect of commercial sterilization on the total nutritive value of milk was studied in five separate experiments.

2. In the first experiment raw and sterilized milks supplemented with minerals were given in equal amounts to pairs of litter-mate male rats. No differences were found in the growth performance of the rats, but the rats on sterilized milk consumed it more readily than their mates on raw milk. This difference was statistically significant.

3. Rats getting limited but equal amounts of milk in addition to a basal diet which supplied only protein, energy and minerals grew better on raw than on sterilized milk.

4. When the basal diet contained in addition 5% brewer's yeast and the milk intakes were the same as in the previous experiment no difference was found between the two groups.

5. Rats receiving raw milk to which 15 g. of cane sugar was added per 100 ml. grew better than rats receiving equal quantities of similarly treated sterilized milk.

6. Rats given raw milk containing 30 g. per 100 ml. of sugar grew as well as the rats on sterilized milk in the preceding experiment, but rats receiving similarly treated sterilized milk took much less milk than the raw milk rats, grew very poorly and some of them developed symptoms of beri-beri.

7. The difference between raw and sterilized milk is discussed and it is concluded that in these experiments on the total nutritive value of milk vitamin B1 was the first limiting factor of sterilized milk.

The work carried out by us on the nutritive value of commercially sterilized milk shows definitely that certain factors are injured in the course of the heat treatment. The biological value of the proteins is slightly but unmistakably decreased, most probably because of the partial destruction of one or more essential amino-acids. Of the vitamins, vitamin C is the most markedly affected. It is decreased by half and, in view of the severity of the heat treatment, it is remarkable that the loss is not greater. The anaerobic conditions which exist during the application of the highest sterilizing temperatures may account for the survival of a part of this labile factor. Vitamin B1 also suffers serious loss, the destruction amounting to 30 % of the original value. Neither vitamin A and carotene nor vitamin B2 (flavin) are affected by the heat treatment. The fate of other components of milk was not studied by us, but experiments on rats on the effect of sterilization on the total nutritive value of milk indicates that vitamin B1 was the first limiting factor of sterilized milk.

An apparatus is described for measuring the elastic and plastic deformations of cheese curd under a compressive load at the time when it is ready for cutting. A figure inversely proportional to shear modulus can be obtained with considerable accuracy, and is believed to serve as the best single criterion of “firmness” in deciding the optimum time to cut the curd.

An enzyme which hydrolyses tributyrin is present in all samples of fresh cows' milk examined. A method has been developed for the determination of the tributyrinase activity of a given milk or fluid.

In milk the enzyme is present in the aqueous rather than the fatty portion. Its optimal range of activity is in the region pH 8·2–8·7. It is rather more thermolabile than phosphatase.

Its concentration in milk varies considerably from cow to cow, and in individual healthy cows there is a fairly regular variation throughout the lactation cycle. It is highest in concentration in colostrum, then the concentration falls to a minimum at about 10 days, rising later to a figure intermediate between this minimum and the colostral value. It shows no sign of increase towards the end of the lactation period.

Its relationship to the “true lipase” of milk is discussed.

The keeping quality of milk is a factor which is of considerable importance from the commercial aspect, yet the relationship which exists between the keeping quality and the bacteriological standards as laid down in the Milk Special Designations Order, 1936, has not been fully explored. Wilson compared the keeping quality at 17·5°C. of samples of mixed morning and evening milk with the reduction times at different temperatures and found, in each case, a relatively poor correlation. Since the samples consisted of mixed morning and evening milk it is not possible to state the age of the milk when the tests were commenced. Much of the Tuberculin Tested milk sold in the Provinces is bottled on the farm, and consequently the milk produced in the morning is bottled separately from that produced in the evening.

Standardization of annatto in aqueous solution has been shown to be unsound, and it has been recommended that standardization be carried out on the basis of the depth of colour produced in cheese itself.

A paper colour standard resembling the German butter standard has been suggested for cheese, the same standard being suitable for the evaluation of annatto solutions for cheese-making.

1. The problem of the physical nature of spreading capacity of butter is discussed, and the advantages of methods measuring individual physical properties in absolute units are given.

2. A simple rheometer is described with which the rate of compression of cylinders of butter can be measured. A simple equation for calculating absolute (mean) viscosities from the data obtained with the apparatus is given.

3. Preliminary experiments, in which temperature control was not as exact as might be desired, nevertheless gave an effective measure of hardness. These are quoted to show the applicability of the method, but they also show the extent to which the phenomenon of “false body” occurs when butter is reworked.

4. A preliminary experiment on the work-hardening of butter is described.

1. Although chemical analysis, bacteriological analysis and graders' reports failed to distinguish the alcohol-glycerol rennet cheese from the brine rennet cheese, the marked qualities in body and texture during making of the alcohol-glycerol rennet curd, and the sterility or low count of the alcoholglycerol extract warrant further trials under practical conditions.

2. Where brine rennet may be suspected as the cause of bacterial faults, the alcohol-glycerol rennet could well be used in its place.

3. Alcohol-glycerolrennets have superior keeping-qualities to brine rennets.

1. Direct steam distillation of cheese does not give a true figure for the volatile acids present in cheese.

2. The fat portion of a cheese has a retarding effect on the distillation of higher volatile fatty acids, although it is possible that a complete recovery of the acid may be effected from the fat if the distillation were to be continued for a sufficiently long period.

3. Cheese protein is capable of a permanent retention of a part of some of the acids present, it being impossible to extract these portions by continued distillation.

4. If direct steam distillation of a cheese is to be carried out the results seem to indicate that by collecting only “twice the original volume” a more accurate picture is gained of the distribution of the acids present in the cheese than would be obtained by distilling to “5 times original volume”, since the retention factor of the protein becomes more significant after “twice the volume” (Fig. 2).

An extraction method for estimating volatile acids in cheese has been described. The values obtained were considerably higher than those given by direct steam distillation.

The abilities of type cultures of lactic acid bacteria to reduce five O/R indicators in plain milk and yeast dextrose milk have been described and the factors influencing their behaviour in this respect discussed. Methylene blue, litmus and safranine appear to be of some diagnostic value for the differentiation of types. There is a marked correlation between rapidity of growth in milk, ability to reduce O/R dyes and the proportion of by-products. This relationship holds not only for the different groups and types, but also for variations in behaviour observed in species kept under laboratory observation. It is suggested that rate of growth is fundamentally related to the amount of by-products and hence presumably to flavour-producing substances such as diacety and acetic acid. Thus in cheese-ripening enforced slowness of growth may be as important as the presence of specific types.

The loss of calcium and phosphorus at various stages in the manufacture and ripening of British hard pressed cheese (Cheddar, Cheshire, Leicester and Lancashire) has been followed. As all the cheese were made from portions of the same bulk milk the results are comparable.

It has been shown that there is remarkably little difference in the values of the hard pressed varieties, but that Stilton contains much less calcium and considerably less phosphorus than any of the other varieties examined.