The records of 2400 cows on test at the London Dairy Show between the years 1922 and 1934 have been examined for the relationship between the gross physiological efficiency of milk production and the factors of breed, size of cow within a breed, actual yield of milk and stage of lactation. (“Gross Efficiency” is here the ratio of energy in the milk to the energy in the digestible nutrients consumed.)

(1) It is shown that among the best representatives of the various dairy breeds there is little difference in gross efficiency of milk production. The lactation stimulus has been bred approximately in proportion to the size of the breed.

(2) Cows, in spite of their greater weight, are more efficient than heifers, and animals milked thrice daily than those milked twice daily.

(3) Within the breed there is a slight though definite tendency for gross efficiency to decrease with increase in live weight.

(4) Greater than any of the foregoing differences in gross efficiency is that which exists within a breed due to differences in actual milk yield.

(5) Stage of lactation has also much to do with gross efficiency. There is a steady decline in efficiency with advance in lactation from 38·75 to 29·25 per cent.

1. A ration for dairy cows which supplied less protein than the recognized protein standards for milk production and contained less lysine than most rations normally used in English farming practice was selected. A comparison was then made between cows receiving this ration supplemented with (a) wheat gluten, a lysine-poor protein, and (b) blood meal, a lysine-rich protein. The addition of blood meal produced no measurable effect on the milk yields, but there was a small and almost significant advantage in the live weights of the cows.

2. In a subsidiary experiment a large increase in the dietary protein produced a very small and non-significant increase in milk yield.

1. A study has been made of the assimilation and retention of nitrogen, phosphorus and calcium by calves fed on raw and pasteurized milks. Sixteen calves were used in the experiments.

2. No significant differences were found between the two types of milk.

3. An examination of the percentage retentions of nitrogen, phosphorus and calcium indicates that milk is relatively deficient in calcium and to a less extent in phosphorus when used as the sole food for calves. The N/Ca balance can be improved by including pasture grass or hay in the ration.

An organism, isolated from discoloured areas in butter and capable of reproducing the colour in artificial culture, is described.

A brown colour, which may probably be attributed to the action of ammonia produced by this organism, diffused through the medium.

A blue-black insoluble pigment, produced only at low temperatures, was concentrated in and around the bacterial cells. The nature of the source of nitrogen influenced the development of this pigment, proteose appearing to be inhibitory.

NaCl in moderate concentration was usually necessary for growth.

1. Van Oijen's modification of the Frost Little Plate method for estimating the bacterial content of milk has been examined and compared with the plate count.

2. The colony counting error of the Van Oijen test is about the same as that of the plate count.

3. From the results of quintuplicate tests it is recommended that 24 hours' incubation at 28°C. be used for the Van Oijen test and 72 hours at 37° C. for the plate test.

4. Thirty-one low-count samples (3000–30,000 per ml.) and thirty-one high-count samples (30,000–300,000 per ml.) were tested in quintuplicate by both methods, and statistical examination of the results shows that at both levels of count the Van Oijen test is significantly more accurate. The Van Oijen results are on the average 1–3 per cent log lower than the plate count and this difference is found to be significant.

5. In the Van Oijen test the results are based on a larger amount of milk than the plate test, and a method is given for testing whether the increased accuracy exceeds the expectation owing to increased size of sample.

6. It is noted that failure of replicate tests to reflect random distribution may be due to the variability of the technique as much as to irregularities in the actual distribution of the bacteria in the sample.

7. The effect of size of sample upon reproducibility is discussed. A true comparison of the accuracy of various methods for assessing the bacteria content of milk samples cannot be obtained unless allowance is made for variation in size of sample as between different techniques.

During the past twenty years the plate count has been largely employed as a means of assessing the hygienic quality of milk. There is no doubt that for this purpose it has proved to be of great value, and the marked improvement which has taken place in the quality of the milk of many producers is largely attributable to its use.

The proteolytic action of rennet, pepsin and trypsin upon milk pasteurized at various temperatures has been investigated. It was shown that the action of these enzymes in pasteurized milk differed from their action on raw milk. The change was especially marked over the temperature range of 150–160° F., and was shown to be due, not to alteration in the protein itself, but probably to some change in the non-protein constituents of milk

The results were applied in a study of cheeses made from raw milk and from pasteurized milk. It was demonstrated, with the aid of cheeses ripened in the absence of bacterial action, that the differences in nitrogen partition which occur between cheeses made from raw milk and from pasteurized milk could be largely accounted for on the basis of chemical alteration produced in the milk constituents by heat treatment—this alteration affecting the proteolytic action of rennet and bacteria upon the cheese curd.

Several defects in canned cream after some months' storage have been classified: (1) “purpling” of the can, due to a film of tin sulphide, (2) pitting of the can, associated with (3) formation of black patches and of black specks in the body of the cream, consisting of ferrous sulphide, stannous oxide or both.

“Purpling” is produced by excessive time and temperature of sterilization, owing to the liberation of active sulphur compounds which attack the tin. Addition of sodium bicarbonate up to 5 g. per gallon has, if anything, a slightly beneficial effect.