The protein requirements for maintenance and milk production are based on the well-known investigations of Kellner, Armsby, Haecker, Savage and others, who recommend feeding standards varying from 0·5 to 0·;8 lb. digestible crude protein per 1000 lb. live weight for maintenance, and from 0·52 to 0·63 lb. digestible crude protein per 10 lb. milk for milk production. A detailed study of the work of these investigations shows that in many instances nitrogen equilibrium has been obtained on considerably lower planes of protein intake: but the figures have been arbitrarily raised, partly to provide a sufficient safeguard against underfeeding, and partly on the assumption that the excess food protein could exert a stimulating effect on mammary secretion. Recent investigations, particularly those of Hills and his associates (l), Perkins (2), Buschmann(3) and Savage and Harrison (4) indicate that the existing protein standards could, in fact, be considerably reduced. The above investigations have, however, been limited to a study of the quantity of protein required for maintenance and milk production, and no account has been taken of the possible effect of variations in the quality of proteins on their utilisation.

1. The production in milk of an aroma resembling that of amyl alcohol was due to the growth of white and orange micrococci, similar to those described as M. caseolyticus by Evans(2).

2. The taint was observed when the cows were housed, but disappeared when they were put out to grass.

3. The source of the causal micrococci was found to be the floor of the cowshed. The taint disappeared when the latter was washed and disinfected.

4. The aroma of amyl alcohol was produced in media containing leucine as the sole organic compound.

The lactose-fermenting coliform organisms in milk and dung have been investigated.

A large proportion of those recovered from raw milk by direct plating proved to be of the Bact. aerogenes type and a number of “intermediates” was also present.

In dung faecal Bact. coli largely predominated, the proportion of Bact. aerogenes being very small.

If the implication of these experiments be accepted it is possible that many of the coliform types found in milk are derived, not from faeces, in which the proportion of aerogenes is small, but from external sources, such as contaminated utensils, and from food-stuffs.

In the course of routine bacteriological examinations of milk carried out at one of the United Dairies pasteurising depots during the past three years, a remarkable lack of constant relationship between the numbers of colonies reported on the 1/10, 1/100 and 1/1000 dilution plates, when standard agar (the Ministry of Health formula) was used, has been observed. When, however, standard agar, enriched with 0·5 per cent, milk, has been used as a plating medium, many of the discrepancies between different dilutions of the same milk have disappeared.

During the past two years, discoloration, owing to its prevalence in Cheddar cheese, has been the subject of much investigation by the New Zealand Dairy Division, and in the present paper are incorporated details of the observations made in this laboratory and in cheese stores in New Zealand and England, together with short reports on the same subject from English laboratories.

To avoid confusion it must be emphasised that the defects dealt with are “bleached,” “pink” and “muddy” discolorations only. The observations do not apply to “black spot” (due to lead or other metallic contamination), nor to “red spots” (due to faulty annatto), nor to “acid cut” bleaching which seems to follow the outline of the original pieces of curd. Muddy or dark discoloration occurs in white and in coloured cheese, but the bleaching and pink discoloration dealt with here are confined to coloured cheese.

The evidence of pH and catalase tests confirms the view that mould growth is closely associated with the production of discoloration in cheese.

The pink discoloration appears to be the result of acids acting upon the annatto colour.

Evidence available from observations and other sources, suggests that the bleaching is chemically a reduction in which changes in the fat play a part.

The muddy or dark discoloration appears to be produced by enzymes (including possibly tyrosinase) which diffuse into the cheese from centres of mould growth and act upon chemical substances present in mature cheese.

1. Records of the percentages of fat and solids-not-fat in the milk supplies received at twelve depots in the counties of Cheshire, Staffordshire, Derbyshire and Leicestershire during the period 1923–31 have been analysed and the results of analysis given in the form of graphs.

2. The yearly averages for the whole area and for the three sections of the area are illustrated and compared with graphs based upon meteorological data (rainfall and temperature) recorded at stations in, or adjacent to, the area.

3. The monthly average figures for the whole period are shown in the form of graphs and compared with graphs based upon data recorded by Richmond.

4. The data upon which this paper is based indicate a positive correlation between rainfall and average composition of milk for each year

Small amounts of heavy metal are distributed between cream and separated milk in proportion to the curd nitrogen, but on completely centrifuging the fat a higher concentration of metal occurs in the cream, showing adsorption of complex proteinate at the fat-globule surface.

The heavy metal entering into butter from cream of different acidities is not affected by the acidity but by the curd-nitrogen content of the butter, but the copper associated with the curd in butter is roughly twice that associated with the protein nitrogen of the buttermilk. This is explained by adsorption of heavy metal on the fat-globule surface, which holds alike in water in oil as well as oil in water emulsion.

The entry of heavy metal into the fat phase in the absence of protein is greatest at neutrality but decreases with increasing acidity. The presence of protein increases slightly the amount of heavy metal entering into the fat owing to adsorptive and buffering effects of the protein at the oil-water interface in the emulsion.

The amount of diffusible heavy metal increases directly with the acidity and runs parallel with the diffusion of hydrogen ions.

The concentration of the ionic form of heavy metal in milk is of a low order, but increase in acidity causes more ionic metal to form. Evidence from potentiometric measurements in milk containing known amounts of heavy metal, or from the addition of milk to a standard copper solution at various acidities, confirms this finding.

In the previous paper(1) it was shown that the heat treatment to which a milk powder is subjected during manufacture may result in the production of two distinct types of protein insolubility, namely insolubility due to denaturation of the protein while still in solution, and insolubility caused by over-heating the milk powder while in a dry state. The insolubility due to denaturation was shown to be independent of the temperature of reconstitution of the milk powder. On the other hand the insolubility due to dry heating was found to vary with the temperature of reconstitution, the protein being relatively insoluble when reconstituted in water held at 20° C, but completely soluble when mechanically stirred for 30 min. in water held at 90° C. It was suggested that this latter type of insolubility might be due to the removal of water of imbibition from the protein particles, since such an explanation would account for the effect of hot water in restoring the solubility of the protein. In the previous paper, however, observations on the effect of temperature of reconstitution were limited to the two extreme temperatures, i.e. 20 and 90° C.

Casein nitrogen has been shown to account for roughly 76 per cent, of the total nitrogen in over 200 samples of normal milk. Samples low in solids-notfat have shown a casein nitrogen percentage below this figure, and by assuming a 76 per cent, level of casein nitrogen as standard, it is suggested that milk may be considered as made up of two fractions, (a) a true-milk fraction and (b) an isotonic diluent. From the distribution of the nitrogen in whole-milk samples it has been possible to calculate on this basis the amount of dilution and the nitrogen distribution in the diluent. Results are given for 38 samples of milk. The chloride content of the diluent has also been approximately arrived at and is approximately isotonic with a hypothetical non-lactosecontaining milk.

The similarity in composition of the diluent either to a modified blood serum or lymph serum or a casein- and lactose-free lacteal secretion has been discussed. Its high chloride content favours its similarity either to lymph serum or a “transudate” or “exudate” closely allied in composition to lymph serum from pathological secretory tissue. The possibility of after-effects of attacks of mastitis causing a chronic catarrhal condition of the udder being the cause of the secretion of this diluent is also discussed.

1. Traces of blood serum albumin have been demonstrated in normal milk.

2. The content of blood serum albumin is increased in many of the milks which are poor in non-fatty solids and there is evidence of some correlation between low non-fatty solids and high blood serum albumin content of the milk.

3. The experimental data support a conclusion that deficiency of nonfatty solids in milk in some cases may be due to dilution of a normal secretion in the udder by a fluid of the nature of oedema fluid, i.e. to a pathological rather than a physiological condition.

4. Some evidence, which obviously needs confirmation, has been adduced indicating that the casein-nitrogen content of milk as determined by Moir's technique may be slightly too high. The accuracy of the globulin figures seems also to be open to doubt.