1. As regards the nutritive value of artificially dried spring grass, the protein appears to be unaffected by the temperature of drying even to the extent of scorching the grass. Early autumn dried grass has a biological value intermediate between spring and late autumn grass, while linseed cake has a very low value.

2. The supplementary effect of the maintenance on the production ration has been shown when hay was substituted for straw in the maintenance ration together with a production protein intake of poor biological value.

3. With an excess of protein in the ration most of the excess nitrogen was excreted in the urine, while both the milk yield and the biological value of the food protein fell considerably. It is possible that, together with an adequate amount of lysine in the protein ingested, a certain mixture of amino-acids is essential before maximum milk yield can be obtained.

4. A study of the nitrogen metabolism shows that high-temperature drying has no effect, whereas marked effects were noted with the early autumn grass and more especially with the linseed cake. The hippuric acid nitrogen output decreased with the high-temperature dried grass, possibly the effect of a loss on drying of benzoic acid. With the high-protein diet an increased excretion of creatinine was noted with no alteration in the creatinine intake. The purin metabolism varies with the total nitrogen excretion, the allantoin increasing markedly in the high-protein period. This is due to an increased intake of purin base.

5. The sulphur metabolism shows the results to be expected from previous publications except in the case of the high-temperature dried grass. It appears that the high-temperature treatment has in some way affected the nature of the sulphur compounds in the grass, with a consequent diminution in the retention.

1. Sucrose and maltose behaved like dextrose, only more specifically in relation to type, in acclerating the rate of growth of lactic acid bacteria in milk. Sucrose was greatly superior to maltose but was never superior to dextrose.

2. Citrate was without significant effect.

3. The sterilization of yeast and dextrose in the medium produced a medium superior to milk + separately heated yeast and dextrose for Streptococcus III. For other types marked differences were not observed.

4. The plant extracts used were found to fall into the following order of ability to accelerate growth: yeast autolysed for 6 days, malt = beer wort, potato, alfalfa, carrot, tomato, clover, yeast autolysed for 2 days, and bean. Malt and beer wort were superior to yeast for some group III organisms.

5. Malt extract and beer wort contain growth factors for some lactic acid bacteria that are not present, or are present only to a small extent in yeast.

6. Alfalfa and clover appear to contain substances specifically stimulating gas production for group III types, especially the streptococci.

7. Normal variations in the content of vitamins B1 and B2 and co-carboxylase in milk do not appear to affect the rate of growth of starter organisms.

Generally speaking, serum and blood do not have a marked effect on the growth of lactic acid bacteria in milk, although certain types appear to be specifically stimulated or inhibited. Heated serum and, to a greater extent, heated blood, usually stimulate growth.

Unheated serum may inhibit certain types, e.g. Str. lactis, when a small inoculum of washed cells is used. Under conditions similar to those in practice, no effect was noticeable. It is unlikely, therefore, that “slow starter” is ever attributable to infiltration of serum or the constituents of serum.

Small amounts of dextrose are without effect on growth (apart from fermentation of the added sugar) and do not initiate the fermentation of lactose.

1. Over 400 samples of spray-dried. milk powder from eight factories operating in England and Scotland have been examined. These samples were taken at different stages of the day's run and were obtained from several types of plant situated in widely different districts. Samples were taken in both the summer and winter months. The samples were, therefore, sufficiently representative to enable general conclusions to be drawn regarding the factors affecting bacteriological quality.

2. In reconstituting milk powders for bacteriological examination it is necessary to ensure (i) that the sample is sufficiently large to be representative, and (ii) that external contamination is avoided during weighing and handling. The use of a 20 g. sample is advocated. Complete reconstitution of the powder is best obtained by shaking the sample with glass beads in a 180 ml. water blank which is contained in a screw-capped bottle. Details are also given of the methods used in bacteriological examination of the samples and for the isolation of pure cultures from them.

1. A survey of evaporated milk and canned cream samples from three condensed milk factories and from general sources has been undertaken to determine to what extent non-sterility occurred in commercial practice. In addition to the examination of sound samples many others have been tested which were obviously defective or which were associated with defective packs. 100% of the tins examined from general sources were sterile. The factory samples, especially those of canned cream, had a lower sterility percentage, although it appeared that this was associated with some special circumstance of operation and that a sterile pack should ordinarily be quite attainable.

2. An account is given of the methods used for sampling the can contents and for the recovery of bacteria from unsterile cans and their identification. The necessity for a large inoculum in such sampling is emphasized, since although the bacteria may survive for many months in the tins, they may be present in small numbers.

3. Data are presented regarding the types of defective samples encountered and the associated bacteriological flora. “Bloats” in evaporated milk and thin bitter and putrid cream were the two main causes of spoilage encountered.

4. By using the heat resistance of the organisms which were recovered from the cans as a basis of classification the. defects have been divided into two groups, namely (1) a mixed general flora which does not withstand high temperatures, and (2) a restricted heat resistant flora which is of the sporeforming type.

The fermentation products of Betacoccus cremoris in neutral milk are acetic acid and carbonic acid. In acidified milk or in mixed cultures of this bacterium and lactic acid streptococci the products are acetic acid, C02, diacetyl, acetylmethyl carbinol and 2–3 butylene glycol. The latter three substances may be called “C4 compounds”. Diacetyl is only formed when an oxidation with atmospheric oxygen can take place. Carbinol is found in aerobic and in anaerobic cultures. It may be reduced to butylene glycol. This reduction is more complete at lower acidity, but also depends on the strain of Betacoccus used.

All these substances are formed from the citric acid of the milk. However, small amounts of acetic acid may be produced from sugar.

From 1 mol. of citric acid are formed: 2 mol. of carbon dioxide, 1–1·5 mol. of acetic acid, 0·5–0 mol. of C4 compounds.

A reciprocal relation exists between the quantities of acetic acid and C4 compounds. When the amount of acetic acid is high the C4 compounds content is low. The higher the acidity of the medium in which the betacocci are cultivated the higher is the amount of C4 compounds. This means that the fermentation in neutral media is the extreme case of the fermentation process. Then the production of C4 compounds is minimal (0) and that of acetic acid is maximal (1·5).

1. An investigation was made of the effect on the casein number of (a) advanced lactation, (b) storage of the milk sample at room temperature and in the refrigerator, and (c) storage of the sample at room temperature after the addition of the following preservatives: potassium dichromate, mercuric chloride, formaldehyde, crystal violet and sodium azide.

2. The casein number method of mastitis diagnosis is not applicable to cows in advanced lactation. It did not distinguish between infected and uninfected quarters, as all quarters in the drying-off stage produced milk with a number below normal. At the end of lactation the mean casein, soluble protein plus non-protein, and total nitrogen contents were 21, 86, and 36% greater respectively than when the cows were in full milk.

3. There was a decrease in the casein number of the milk samples on keeping at 16–18° C. or with preservatives owing to the hydrolysis of casein to proteose-peptone and non-protein nitrogenous substances. For the diagnosis of mastitis from the casein number, samples should not be kept at room temperature for more than a few hours before analysis. Keeping at 0–2° C, and at room temperature with the addition of 0·2, 0·05, and 0·01 g. potassium dichromate, formalin or mercuric chloride respectively per 100 ml. of milk, prevented significant reduction of the casein number for 24–48 hr.

1. Spray-dried (Kestner process), roller-dried and evaporated milks were prepared commercially from one batch of raw milk.

2. The biological value of the proteins (nitrogen), vitamin B1 and the growth-promoting properties of the milks were measured by tests on rats.

3. Vitamin A and carotene, riboflavin and vitamin C were measured by physical and chemical methods at intervals in the course of storage for a year.

4. No significant difference was found between the biological values of the proteins (nitrogen) of the processed milks. The values ranged from 80 for evaporated milk to 84 for spray-dried milk.

5. The proteins (nitrogen) of evaporated milk were significantly less digestible (true digestibility 91) than those of spray-dried milk (true digestibility 94). The difference between either of those and roller-dried milk (true digestibility 93) was not significant.

1. A rapid method for determining the peroxide value of the fat contained in whole milk powders is described.

2. As estimated by this method the peroxide value is only about 90% of the true value, but in many researches where the method would be applied, it is the relative rather than the absolute peroxide value which is required. Consequently the disadvantage of a slightly low estimation is far outweighed by the rapidity of the method and the ease and reliability with which it can be performed.

The oxidation of the fat of butter during cold storage has been studied by measuring the fat-aldehyde value of the fat. A direct relationship was found between this value and the grade after storage.

It was found that acidity, starter organisms, salt and low-pasteurization temperatures each favour the oxidation. Neither diacetyl nor acetoin influence the oxidation.

The results indicate the presence in ripened pasteurized cream and in unripened raw cream of a fat-oxidizing enzyme which is most active at low pH values (about 5) and high salt concentrations.

Simple and rapid methods have been devised which utilize the minimum of apparatus and material for the routine bacteriological testing of butter. These involve the preparation of microplate cultures to obtain counts of total bacteria, “heat-resistant” bacteria, lipolytic organisms, yeasts, moulds; Grimes's method as a measure of the coliform content is also used.

The method for counting colonies of lipolytic bacteria is based upon their ability to produce round each colony a halo of white solid fatty acids in place of the clear glistening fat globules.

The new methods have been exhaustively compared with those hitherto accepted, and have been found to give satisfactory and reliable results.

A variety of comparisons has been carried out to improve still further the methods in use and to provide additional information about the nature of the bacteria contamination present in the butter. The roll-tube method seems preferable to the microplate for mould counts, and is quite suitable for yeast counts.

The results obtained confirm the view expressed by Wood & Thornton(6) that yeast and mould counts provide an inadequate criterion of factory sanitation, and should be supported at least by the total count of bacteria.

The employment of these methods has enabled large numbers of samples to be dealt with. Thus samples from most of the principal New Zealand butter factories have been regularly tested. The information so obtained has been of material value to the Dairy Division's Instructors in drawing attention to factories where sanitary conditions left room for improvement.

“Open” cheese were shown to evolve carbon dioxide much more rapidly than did “close” cheese. From open cheese lactobacilli or betacocci capable of producing carbon dioxide relatively rapidly could be isolated. The addition of such organisms to cheese milk resulted in the development of slit openness in the cheese. The most common types causing slit openness appeared to be gas-producing lactobacilli.

The reproducibility of Scott Blair's method for measuring curd firmness has been tested and measurements of the “firmness” of cheese curds immediately prior to cutting have been made and related to an expert's opinion. Contrary to her beliefs it was found:

(1) that the mean firmness for normal Cheshire and Double Gloucester curds was the same as that for normal Cheddar curds,

(2) that normal curds, regardless of type, were softer in the summer months than in the winter.

Though confident opinions are often expressed on very small differences in firmness, the smallest difference in modulus which can be correctly appreciated appears to be of the order of 8%.

1. Some existing types of rennet tests are briefly reviewed.

2. A viscosity type of rennet test is described and results from its use are given.

3. A mathematical treatment of the problems involved is given, which leads on to

4. Construction of graphs showing progressive variation in “Dying away of amplitude”, “Logarithmic decrement” and “Viscosity coefficients” of milk under the action of rennet. Since viscosity determinations on liquids and gases have been commonly carried out with a disk type of viscosimeter, such a type is now introduced and similar graphs constructed from observations during its use. A close similarity in graphs to those furnished by the cylinder type of viscosimeter is obtained. The cylinder type of apparatus, we find, is more convenient in use with milk in reference to rennet action.

5. Arising from the graphs a more precise method of terminating a rennet test with the present type of apparatus is indicated.