1. The denaturation of albumin and globulin took place rapidly in samples of milk heated at temperatures of 75°C. and above, and was complete in approximately 60, 30, 10–15, and 5–10 min. at 80, 90, 95, and 100°C. respectively.

2. There was no change in the non-protein nitrogen content of milk on heating at temperatures up to 100°C.; on continued heating at 95 and 100°C. extremely small amounts of proteose were produced by hydrolysis of protein.

3. In milk heated at 115 and 120°C. the denaturation of albumin and globulin was followed by appreciable hydrolysis of protein, which resulted in considerable increases in the proteose and in the non-protein nitrogen contents.

1. The investigation was for the purpose of ascertaining the cause of the variations previously noted by the author as occurring in mare's milk.

2. Determinations have been made of the composition of the milk of eight Shetland ponies and one Clydesdale mare throughout the lactation period, with observations on the milk of numerous thoroughbred mares. The constituents estimated were the total solids, solids-not-fat, protein, fat, lactose, total ash, CaO, P2O5, and chlorine. The CaO, P2O5 and chlorine percentages in the ash of the milk were also determined. The freezing-point and pH were recorded in a number of samples. The animals were kept under natural conditions at grass.

3. It was found that as lactation advanced the percentage of total solids, lactose and fat of the milk increased in a linear manner, whereas the percentage of solids-not-fat, protein, CaO, and P2O5 decreased linearly.

4. The regression of the total solids and the chlorine was parabolic in character as also was that of the chlorine-lactose index.

As a member of Committees of the Empire Marketing Board and subsequently of the British Standards Institution, the author has had experience in methods of milk testing which has led to the discovery of a simplified test for butterfat, which may be of value in filling some of the gaps in the application of the present known methods.

Milk was obtained simultaneously from cows on early pasture and from stall-fed cows receiving winter rations. By suitable blending of the morning's and evening's milkings of each milk the fat content of the two milks was equalized daily. A part of each milk was then pasteurized in the laboratory by a “holder” method. The total nutritive value of the milk was measured on rats in two separate experiments. In one the milks, supplemented with iron, copper and manganese, were fed as an exclusive diet. The four types of milk were given to twelve groups of litter-mate male rats, the intake being equalized within each group. The experiment lasted 8 weeks, and at the end no difference was found in gain in weight, body length, general appearance of the rats or composition of the carcasses. The palatability of the milks as gauged by the refusals of the rats was investigated by various statistical methods, which showed that summer milk was probably more palatable than “winter” milk, but that pasteurization had no effect.

In the second experiment the intake of milk was limited to 20 ml. daily, but the rats were given in addition unlimited access to a basal diet of casein, sugar and salts. This experiment was also carried out on groups of four litter mates (four groups of does and seven groups of bucks). After 8 weeks 5% brewer's yeast was added to the basal diet, resulting in a marked increase of the growth rate of all the groups. At the end of the 8 weeks, the gains in weight, intakes of basal diet, and gains per gram of solids ingested were compared. The only statistically significant differences were in favour of pasteurized summer milk when compared with summer raw and with “winter” pasteurized.

1. The means and standard deviations of analytical data obtained from fifty-four samples of mixed milk (alternate a.m. and p.m.) and whey from the College herd of Dairy Shorthorns are presented in Table I. The samples were taken at intervals during the period late September 1935 to November 1936.

2. While no outstanding differences in composition are evident between morning and evening samples, the time of rennet coagulation was appreciably greater with the evening's samples. Evidence is presented to show that the longer time of cold storage of these samples must be regarded as a contributory cause of this effect.

3. In the discussion of the mean values, special treatment has been given to the partition of calcium and phosphorus between the four phases, soluble and insoluble, organic and inorganic. The caseinogen values are examined in the light of current theories.

1. The literature on the soluble protein fraction of milk has been reviewed to show the difficulties that are encountered in attempting to decide whether the fraction consists, as is usually supposed, of lactalbumin and lactoglobulin only, or whether it consists partly of secondary proteins of a proteose-peptone nature.

2. It has been shown that on boiling the casein-free filtrate of milk, maximum coagulation of albumin and globulin occurs at a pH. of 4–75–4–80. At this pS. prolonged boiling does not cause hydrolysis, and the amount of albumin and globulin N coagulated represents about 70 per cent of the total soluble protein N of milk.

3.By precipitation of the casein-free nitrate of milk with various con- centrations of trichloracetic acid, a partition of the soluble proteins has been effected which strongly suggests the presence of proteose-peptone substances to an extent in agreement with the results of heat coagulation.

4. The maximum amount of albumin and globulin rendered coagulable by heating milk itself has been determined by precipitating denatured albumin and globulin along with casein at pH. 4–7. This maximum represented an average of 76 per cent of the total soluble protein N in a series of normal milk samples, and reasons have been given for considering this maximum as the total of true albumin and globulin present.

5. The conclusion has been reached that the soluble protein fraction of normal fresh milk is composed of approximately 76 per cent albumin and globulin, and 24 per cent proteose-peptone substances.

1. The effect of heating on the creaming power of milk and the role of truly hydrophilic colloids in increasing the creaming power of raw and of heated milk are discussed. The suggestion is made that a proper understanding of changes underlying the reduced creaming power of heated milk has been handicapped by a lack of reliable data on the extent to which the hydrophilic colloid content of milk is reduced by denaturation of albumin and globulin.

2. Information is obtained concerning the relationship between the denaturation of albumin and globulin and the reduction in creaming power from a series of determinations of the amounts of protein denatured, and of the changes in creaming power produced, by heating samples of the same milk for 30 min. at temperatures of 57·5, 60·0, 61·5, 63·0, 65·0, 67·5, 70·0, 74·8 and 80·0° C.

In an ad libitum feeding experiment the greater growth of a group of animals may be due either to superior availability or to superior palatability of their diet. To distinguish between these two factors it is necessary to eliminate the effect of superior palatability by equalizing the food intake of corresponding animals. If the quantity offered is so small that it is always consumed entirely, the range of application of the experiment is restricted to conditions of substarvation, and at the same time the possibility of obtaining from the results any evidence of difference of palatability is sacrificed. The ration plan must therefore be designed to be as liberal as possible subject to the conditions that the aggregate food intakes are equalized in pairs (or larger groups), while at the same time the animal with the smallest appetite of each pair (or group) is always on the border-line of refusing a little of its portion. In the first set of experiments described in the preceding paper (1) a system of this kind is employed.

1. Acetylmethylcarbinol in cream is partly destroyed by neutralization and pasteurization, but the diacetyl content is practically unchanged.

2. Diacetyl and carbinol are retained in butter with the butter-milk fraction.

3. Diacetyl is present in butter: (a) sweet-cream 0·05 p.p.m., (b) “mild starter” 0·3–0·4 p.p.m., and (c) “high acid” 1·5 p.p.m. The diacetyl content remains fairly constant during 3½ months' storage at 14° F.

4. Diacetyl in butter does not affect the keeping quality or vitamin A content.

5. The diacetyl content tends to increase when butter is held at 40° F. for several days after manufacture. The change is not caused by oxidation with air, but is probably due to dehydrogenase activity of the “starter” organisms or their enzymes.

6. Experiments with butter “starters” are described.

1. Experiments were carried out during the years 1931–5 in which mice on a basal diet of raw milk and white-flour biscuit were compared with mice on a similar diet except that the raw milk was replaced by commercially holderpasteurized (145–150° F. for 30 min.) milk belonging to the same batch. Each group of mice comprised in aggregate about 1100 animals, which were usually 4–6 weeks old at the commencement of observation. For reasons given on p. 206 no attempt was made to standardize the volume of milk consumed by the individual mice. Except in the preliminary experiments, when the milk was given in excess, the amount supplied was regulated more or less in accordance with the requirements of the average animal.

1. Bull calves from tuberculin-tested Ayrshire herds were fed on raw or commercially pasteurized milk up to 12 weeks of age, in amounts strictly in relation to their body weight. This diet was supplemented from the eighth week by hay at the rate of 2/3 lb. per head per day.

The milk used was mixed milk from untested herds, the raw and pasteurized milk being derived from the same bulk sample. The quality of the milk was controlled by daily butterfat and phosphatase tests and by inoculation of grouped daily aliquots twice weekly into duplicate guinea-pigs.

2. The total number of calves used in the experiment was ninety-two. Of these, forty-two received pasteurized milk and fifty raw milk. Nineteen calves died before completion of the experiment, five in the pasteurized milk-fed group and fourteen in the raw milk-fed group. The mean ages of these calves at death were 44 and 27 days respectively.

Seventy-three calves completed the full 12 weeks of the experimental feeding. Of these, thirty-seven received pasteurized milk and thirty-six raw milk. The former group showed a mean percentage gain in live weight of 80·2 ± 3·1, the corresponding figure for the latter group being 74·5 ± 2·7. The difference, i.e. 5·7 + 4·1, was not significant. Reasons are given for the relatively low growth rate observed.

3. No appreciable differences were noted in the skeletal growth of the two groups. Marks awarded by experienced stock judges showed consistent differences in favour of the pasteurized milk-fed group, although the significance of such differences cannot be assessed.

4. Inoculations of grouped daily aliquots of raw milk twice weekly into duplicate guinea-pigs resulted in finding viable tubercle bacilli in 70% of the samples and Br. abortus in 38% of them. The pasteurized milk samples were uniformly negative to both tests.

The differences in tuberculous infection of the two types of milk were reflected in the results of tuberculin tests and post-mortem examinations on the calves at the conclusion of the experiment. Twenty-four out of thirty-six calves fed on raw milk reacted to the test, and the presence of tuberculous lesions was confirmed in twenty-three by post-mortem examination. One calf in the pasteurized milk-fed group reacted to the test, but exhaustive post-mortem examination and inoculation of glandular material into guineapigs failed to confirm the presence of any tuberculosis.

5. This work has failed to show any significant differences in the nutritive value of raw and of pasteurized milk for the rearing of young calves. The use of pasteurized milk, however, had a clear advantage in that it preserved the animals from infection through drinking milk containing living tubercle bacillli.

Apart from mastitis milk there appear to be two types of soft-curd milks:

(1) Milks of individual cows which throughout a lactation or throughout their lives persistently give soft-curd milks. Such milks readily respond to additions of acid and appear to be due to the breed and individuality of the cow and not to any abnormality.

(2) Milks of cows or herds which, though normally giving a satisfactory coagulum, suddenly become rennet-resistant for a certain period. Such milks are more difficult to deal with as in general they do not respond to additions of acid unless these additions are large.

There is little evidence available to show whether the two types are regularly related, but some individual cows in a herd do produce soft curd milk of the type which is unresponsive to the addition of acid regularly throughout a season when the majority of the cows in the herd are giving normal renneting milk. In the work described above on individual cow's milk there has been no attempt to classify the milks according to the effect of acid on the coagulation, although it is now realized that such a course would have been desirable.

Traces of certain metallic contaminants (copper, iron, lead, zinc, aluminium and manganese), when added at the rate of 3 and 7 p.p.m. to milk used for the manufacture of Cheddar cheese, cause certain flavour (and colour) defects in the matured cheeses, of which, however, no indication is given when the cheese is plugged and graded at about 14 days after manufacture.

The distribution of copper, iron, manganese and lead between curd and whey during the cheese-making process is recorded and the action of traces of various metals on the acidity development in a typical "starter" culture has been followed.

The discolorations noted for copper- and iron-contaminated cheeses are considered to be due not to the formation of their sulphides (although this is the case for lead discoloration), but to the atmospheric oxidation of a colourless metal: protein complex.

A Preliminary investigation of certain defects and the results of the short time storage of experimentally processed batches of cream have been reported in a previous communication(1). The results of further storage of these batches and of additional batches utilizing different stabilizing agents are now presented. It is thought that a complete picture of the corrosion phenomena and the main factors influencing them have now been obtained.

1. In a series of virulence experiments a comparison was made between the resistance to infection of 551 mice fed on raw and 495 mice fed on pasteurized milk, each dietary being supplemented by a mineral mixture and a whiteflour biscuit. In one set of experiments the mice were inoculated intraperitoneally with about 100 or 1000 living Bact. typhi-murium and observed for a fortnight; in another set they were fed by the mouth with about 100–200 million living organisms of the same strain and observed for 4 weeks. All animals dying during, and all survivors killed at the end of the experiments were bacteriologically examined for evidence of specific infection.

2. In the intraperitoneal inoculation experiments the results obtained with the raw and pasteurized groups respectively were as follows: Proportion of animals dying of specific infection 51·83 and 51·20 per cent; proportion of all animals found to be specifically infected at death or when killed 95·29 and 91·57 per cent; average survival time of animals dying of specific infection 8·06 and 6·93 days. The proportions of animals dying of specific infection when standardized for weight distribution were 55·1 and 50·6 per cent respectively.

Various strains of lactobacilli isolated from Cheddar cheese were added to the milk employed in cheese manufacture. Different strains of these organisms were found to impart specifically characteristic flavours to the cheese. The range of flavours developed included both desirable and objectionable types, many of which are commonly encountered in commercial cheese, e.g. “pleasant aromatic”, “diacetyl-like”, “metallic”, “bitter”, “unclean” and “fermented”.

The inoculation of cheese-milk with natural mixtures of lactobacilli from mature cheeses led almost always to the development of unclean “fermented” flavours. The causative strains of lactobacilli were isolated and shown to be of frequent occurrence in normal mature cheeses but under ordinary circumstances the actual numbers of these bacilli present in most cheeses were too small to spoil the flavour.

The properties of commercial annatto solutions have been examined from the point of view of the cheese-making process.

(1) The effect of initial colour strength, pH of the medium and distribution during manufacture are recorded.

(2) Methods are described for the extraction of the annatto colour from milk products.

(3) The effects of old annatto solutions, metallic impurities (copper and iron) and sulphydryl are shown.

(4) It is suggested that the mechanism underlying the development of “bleached” and “pink” discoloration in cheese is an oxidation process, and the effect of oxidation on annatto solutions has been studied in some detail.

(5) Suggested standards for annatto extracts for use as cheese colours are appended.

1. Three organisms have been isolated from defective commercially-canned cream which, on inoculation into normal cream, cause bitterness and thinning.

2. These organisms are described and are shown to be strains of B. subtilis. Their spores are capable of withstanding temperatures up to 120°C. for as long as 40 min.

3. The rate of development of bitterness and thinning in experimentally inoculated cans is shown to vary with the culture used and with the temperature of incubation.

4. Both bitterness and thinning are associated with the breakdown of protein, as indicated by determinations of the non-protein nitrogen and of the peptone and subpeptone fractions.

5. The alterations in viscosity do not appear to be due to any fundamental change in the structure of the cream, nor to differences in the degree of clumping of the fat globules.

6. The applications of the results in commercial practice are discussed.

The paper embodies an examination of the possibility of sex-linked genes affecting the transmission of milk yield. To reduce environmental effect the study was restricted to three herds of the English Dairy Shorthorn breed, and each herd was considered as a unit. Fisher's Squared Difference method was used.

The lumped results confirm previous work to the effect that the paternal grandsire has a lesser effect than the maternal grandsire. In this respect the figures for one herd did not agree with the other two.

The largest herd (which showed this difference) was divided into two sections, high and low yielders. These sections did not show any difference in the relative effect of the two grandsires. The implications of this are discussed, and it is tentatively suggested that if sex-linkage operates it has a considerable effect of some 250 gallons on an average yield of 600 gallons.

It has been shown by experiments in milk that the enzymes of commercial rennet in conjunction with the lactic acid bacteria occurring in Cheddar cheese can bring about protein breakdown similar in extent to that found in the ripe cheese as far as the non-protein nitrogen is concerned. The amino nitrogen produced is, however, much less than in cheese. This may be ascribed to the higher pH of cheese as compared with that of the milk cultures, since acidity adversely affects the peptidases present. Attention is drawn to the differences between the conditions.