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. As regards their nutritive value for milk production, the proteins of spring grass are markedly superior to those of autumn grass. This is shown not only from a study of milk yield, but from the increased excretion of N and S in the urine, the increased creatine excretion, and the lower biological value given by autumn grass.

2. A study of the N and S metabolism of cows receiving fresh and artificially dried grass fails to reveal any significant differences in the nutritive value as a result of artificial drying. There are no significant differences between the biological values of the proteins of fresh and of artificially dried autumn grass. A comparison of the mean biological values of the proteins of fresh and of artificially dried spring grass indicates that the latter has an inferior value for milk production, but the differences largely disappear when the biological values are calculated to a common standard.

Four cows, all giving milk low in solids-not-fat, were used for the experiment:

1. The change from winter rations to pasture produced a decided increase in the solids-not-fat percentage and milk yield.

2. Well-balanced rations fed to the cows during two lactations showed a small rise in the milk yield and solids-not-fat during the second lactation, but did not increase the solids-not-fat to above the 8·50 per cent, limit.

3. Feeding a high protein ration of albuminoid ratio 1:2·76 produced no change in milk yield or casein, decreased the solids-not-fat and lactose, and increased the total milk nitrogen and albumin and globulin nitrogen.

4. Feeding a high carbohydrate ration of albuminoid ratio 1:9·90 did not affect milk yield, fat or ash, but decreased slightly the solids-not-fat.

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.

The influence of mastitis and of Br. abortus infection, separately and combined, has been observed in two tuberculosis-free herds during the years 1929–31 and 1930–4 respectively. Actual abortions in these herds were few, but many cows were affected with Streptococcus mastitis in a subclinical form. The results, comprising the examination of 180 lactations in Ayrshires and 193 in Friesians, have been considered in relation to the results of others who have investigated the influence of Br. abortus infection on the yield.

When all the lactations of all cows were considered, the average reduction in yield per lactation was 954 lb. due to mastitis and 1685 lb. due to mastitis and abortion combined. Among the Ayrshires of one herd the average reduction due to mastitis was 892 lb.

In the ruminant, the main tertiary nitrogenous metabolite of all the tertiary nitrogenous bases examined is trimethylamine oxide. Small traces of trimethylamine and insignificant traces of mono- and dimethylamine also occur in cow's urine. The nitrogen of simple bases (trimethylamine and trimethylamine oxide) is almost quantitatively and rapidly excreted as trimethylamine oxide. With betaine, choline and the methyl ester of dimethylaminoacetic acid, only from 14 to 43 per cent, of the nitrogen is excreted as trimethylamine oxide, the amount so excreted depending on the level of nitrogen intake, the nature of the base fed and the degree of accommodation of the animal to the base fed.

The rates of excretion of the tertiary metabolite show well-defined peaks depending on the nature and amount of the base fed. The feeding of 100 g. of betaine would show a peak of excretion at about 4½ hours after feeding. The importance of the time interval between feeding and milking is discussed from this aspect. No unchanged betaine was be detected in the urine.

1. The titration method for the estimation of colloidal tricalcium phosphate in milk was found to agree closely with the determination of total colloidal inorganic P2O5.

2. The method was used to study the solution of tricalcium phosphate in milks of rising acidities.

3. Close agreement was obtained between the actual increase in total P2O5 in the wheys of souring samples and that calculated from the disappearance of tricalcium phosphate as found by the titration method.

4. The discrepancy between the actual increase in whey calcium in such cases and that calculated from the titration figures was attributed to the solution of calcium from the calcium salt of caseinogen. From figures so obtained it would appear that colloidal calcium phosphate dissolves with greater ease in milk than the calcium of the protein salt.

5. A linear relationship was found to exist between the ordinary titration value of milk and the three other values used in this estimation, and also between the curd acidity and milk acidity.

6. Average figures are given for the tricalcium phosphate content of the samples studied and for the various titration factors.

1. A method has been described for obtaining milk anaerobically from the udder.

2. A technique for transferring anaerobically drawn milk to an electrode vessel for the determination of oxidation-reduction potentials under anaerobic conditions has been described.

3. A technique for transferring anaerobically drawn milk to a van Slyke apparatus for gas analysis has been described.

4. The total CO2 of cows’ milk is about half that of their blood plasma.

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.

1. Determinations have been made of lactose and lactic acid in whey, curd and curd juice throughout the cheese-making process.

2. The effect of adding salt to curd at various stages of the process on the concentration of lactose and lactic acid in the whey has been investigated.

3. The rate of penetration of salt into curd has been determined, and it has been shown that by the time the cheese is normally hooped but little salt has reached the centre of each curd strip. Within 12 hours after hooping the distribution of salt is substantially uniform.

4. It has been shown that the conversion of lactose to lactic acid by starter bacteria in the cheese vat is almost quantitative.

5. Evidence has been brought forward indicating the presence of bound water in cheese curd.

6. It has been shown that a Donnan equilibrium controls the partition of electrolytes between curd and whey.

No sulphydryl compound in free solution could be found in cow's milk. It is suggested that the positive nitroprusside test obtained in milk treated with sodium cyanide is traceable to the cystine in the protein complex.

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. Bacteria may play but an insignificant part in the reduction of methylene blue in milk, though their de-oxygenating effect may be of influence in the commercial application of the test.

2. Milk as it exists in the udder, or milk drawn anaerobically, reducesmethylene blue almost instantaneously, whereas the same milk exposed to oxygen will usually take more than 10 hours to reduce.

3. The oxidation-reduction potential of anaerobically drawn milk is much lower than the same milk exposed to oxygen, and in accordance with its behaviour toward methylene blue.

4. Evidence is given for the presence of a redox system, present in low concentration, as responsible for the reduction of methylene blue.

5. Although the addition of small amounts of cysteine or glutathione to milk leads to the reduction of methylene blue, their absence from milk excludes them as possible factors in the normal reduction.

6. The possibility that lactoflavin may furnish the redox system is suggested.

7. The reduction of methylene blue in milk is catalysed by light in the visible spectrum.

Various types of proteolytic cocci, including several acid-proteolytic strains, have been isolated from foremilk and rennet extract (l) and subsequently from ripened Cheddar cheese. A study of the proteolytic activities of these cultures in milk forms the subject of this investigation.

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.

1. The application of the method of Somogyi to the determination of the reducing sugar in milk, with a precision of ± 0·36 per cent., is described.

2. Washed yeast does not ferment lactose and does not add reducing material to tungstic acid nitrates.

3. The reducing substance in milk removable by yeast can be determined with an accuracy of ± 3 per cent.

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.

Since the publication on physiological youth in bacteria by Sherman & Albus(1), many workers have demonstrated that the resistance of microorganisms to environmental changes is greatly influenced by the age or stage of growth of the organism under consideration.

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.