1. A 142-day feeding experiment with twenty-one dairy heifers aged 7–17 months is described.

2. The addition of 0·127 lb. per animal per day of urea to a diet supplying a limited amount of protein resulted in an extra daily live-weight increase of 0·24 lb. per day. This increase was statistically significant and the animals appear therefore to have utilized the urea nitrogen in their metabolism.

3. Animals receiving the same quantity of additional nitrogen in the form of protein showed slightly better live-weight gains than those receiving the urea; although the difference was not significant it seems probable that the protein was a more efficient nitrogen supplement than urea.

We have dealt in a previous communication (1) with the effects-of commercial pasteurization on the nutritive value of milk. We present here the results of an enquiry into the nutritional effects of the more drastic heat treatment to which milk is subjected during commercial sterilization. There is no legal definition of either sterilized milk or of the process of sterilization, but in commerce it is customary to apply the term to milk which has been heated to at least 212° F. for varying lengths of time.

1. It was planned to study the variations of the protein content of milk during the lactation period.

2. The total protein nitrogen and the casein nitrogen were determined by approved methods in about 380 weekly samples of milk taken from twentyseven individual cows of different breeds and at different stages of lactation, from February to July 1937. The albumin+globulin nitrogen was calculated in each case by difference.

3. The statistical analysis of the figures was made by the methods of “factorial arrangement” and by “pairing”, and also by the estimation of the 95% probability range of the mean of the figures available for each week of lactation.

4. It was found that the percentage of total protein nitrogen decreases very significantly from the beginning until the 4th week of lactation, and then rises slowly until the end of lactation, the rise being more pronounced to wards the end. The same was true for casein nitrogen and for albumin+globulin nitrogen, but with the latter only the decrease at the beginning and the rise at the end were sharp. The rise for the rest of the lactation curve, although it did exist, was very slow.

5. The lactation curves for the yield of total protein nitrogen, casein nitrogen and albumin + globulin nitrogen were practically parallel with the lactation curve for the yield of milk.

6. The correlations between the yield of milk and the percentages of total protein nitrogen, casein nitrogen and albumin + globulin nitrogen are studied and the correlation tables with all details are given for each. It is noteworthy that the regression lines are not linear and that with a poor milker an increase of 1 lb. in yield of milk corresponds to a relatively high decrease in the percentage of protein nitrogen, whereas with a high milker this decrease is relatively much smaller.

7. The correlations between the yield of milk and the yield of total protein nitrogen, casein nitrogen and albumin + globulin nitrogen are examined and the correlation tables are given. It is shown that there is a close correlation between the yield of milk and its protein content, from which the conclusion is drawn that a very low protein food does not decrease the percentage of protein in milk as one might expect, but decreases the yield of milk and increases the percentage of protein in milk. On the other hand, an increase of adequate protein in the ration may raise the yield of milk if it is not at its maximum level.

8. It is emphasized that the above conclusions are drawn from a study carried out on a group of cows, and may not be strictly applicable to individual cows.

Variations in protein yield of a cow are due to changes both in her yield of milk and in the percentage of protein in her milk. If it were possible to have, for each day of lactation, figures for the yield of milk and its percentage of protein, the estimation of lactation yield of protein would be easy, but in practice this is not possible since the determination of protein in milk is a long and laborious process.

1. An experiment is described in which comparisons were made between the effect of (a) mangels (control feeding), (b) artificially dried grass, (c) sprouted maize, and (d) kale used as dietary supplements on the production and nutritive properties of the milk of dairy cows.

2. No significant differences were found between any of the foods in their effect on yield of milk, or its content of fat or solids-not-fat.

3. The feeding of kale and of artificially dried grass markedly increased the colour and vitamin A content of the milk, but sprouted maize had no more effect in this respect than mangels.

4. As compared with the feeding of mangels, sprouted maize and artificially dried grass had no measurable effect on the vitamin B complex level of the milk.

5. The vitamin B2 (complex) level was more variable and was lowest in the milk from the sprouted maize cows. It is not known, however, whether the difference was due to the feeding or to differences in the cows themselves.

6.The same statement applies to figures for the vitamin C level which was highest in the sprouted maize milk.

7. The growth-promoting properties of the milks produced on mangels, artificially dried grass and sprouted maize were compared. The milks were fed, supplemented either with minerals alone, or with minerals plus sugar as a source of energy. In one series of experiments the milks were given adlibitum, in another the intake was “equalized.” No differences were found and it is concluded that under English conditions, this technique does not disclose the presence in milk of a new essential factor.

1. The biological values and true digestibilities of the proteins of raw and commercially sterilized milks from the same bulk have been compared on rats by the method of Mitchell.

2. For raw milk a biological value of 84·3 and a true digestibility of 96·4 were obtained, while the figures for sterilized milk were 79·1 and 95·3 respectively.

3. Statistical tests showed that the difference in true digestibility was not significant but that the lowering of the biological value by about 6% could be ascribed to the effect of the heat treatment, the odds against chance factors being 625: 1.

1. In experiments in which the biological value of the proteins was measured spray dried skimmed milk was fed separately from or mixed with a basal “nitrogen free” diet.

2. At a 6·9% level of protein (N x 6·38) intake the first method of feeding yielded a biological value of 87·2, the second of 90·3. The difference was not statistically significant (odds of 9: 1 against chance factors).

3. The findings do not account for the low biological value reported by us previously for the proteins of raw liquid milk.

1. The yield and composition of the milk secreted during a 12-day fast is recorded. The solids-not-fat, the nitrogen partition, the chloride, lactose, fat and phosphatase contents are discussed.

2. The presence of an unknown substance in the “abnormal” milk obtained from two of the cows is recorded, and it is shown that similar amounts of an unknown constituent must also have existed in the starvation milk analysed in the course of their work by Overman & Wright(i). The nature of this substance has not yet been elucidated.

3. Certain substances in the blood were estimated before, during and after the fast, and the possibility of relating changes in them with corresponding changes in the milk is discussed.

An account has been given of observations made for over two years on the composition of the milk of the breeds of goat distributed throughout Great Britain. The average percentages of fat and solids-not-fat in the milk of the breeds, together with their standard errors, are recorded. The frequency with which evening and morning samples fell within specified limits of these constituents is indicated for each breed, and diagrammatically for all goats. Detailed analyses of the milk of each breed are given, with the maximum and minimum values encountered and the standard errors of the average figures. Comparison is made of the composition of the milk of the goat with that of the cow. The effect of stage of lactation on yield of milk and on percentages of fat and solids-not-fat are shown by means of curves. the effect of age on the yield and composition of milk is indicated. The average yields per lactation for each breed, based upon the records of animals officially recorded during the last ten years are noted.

1. In a field investigation covering twenty-nine herds, an average of 19·5% of the animals in milk during the first three months of 1937 were yielding milk low in solids-not-fat, estimated by the routine method, at two consecutive milkings.

2. Of the low solids-not-fat cows which were not stale, evidence of mastitis infection was found in an average of 61·5% of cases. Re-examination of some negative animals suggests that the total infection amounted to about 70%.

3. There were apparently at least twice as many “subclinical” cases of mastitis as clinical cases.

1. The vitamin A and carotene content of raw milk have been compared with that of milk from the same bulk after it had been commercially sterilized.

2. For this purpose the fat was obtained by ether extraction from eleven samples of raw milk and from eleven corresponding samples of sterilized milk. As the sterilized milk had been previously homogenized it was not possible to churn it.

3. The vitamin A and carotene content was estimated by colorimetric (Lovibond tintometer) and by spectrophotometric tests.

3. The vitamin A and carotene content was estimated by colorimetric (Lovibond tintometer) and by spectrophotometric tests.

4. The results showed that the efiect of the heat treatment was negligible, neither method demonstrating a loss in vitamin A, while for carotene only the colorimetric method indicated a loss of about 2 %.

5. The vitamin A and carotene contents of sterilized milk were not decreased after storage for several weeks in a cool dark place.

On injecting a neutral solution of pure trimethylamine oxide into two quarters of an udder, the quarters increased in turgidity up to 2·5 hr. and then relaxed. The oxide diffused rapidly out of the quarters during the third and fourth hours after injection and a maximum concentration was shown in the urine at the end of the third hour. In a period of 8·3 hr., 76 % of the oxide available for diffusion was recovered from the urine.

The milk obtained 7 hr. after injection contained 7–8 mg. % of tertiary nitrogen, but the secretion had not in that time regained normal composition owing to the interference with the natural functioning of the quarters.

The frequency distribution of the chloride contents of 7802 samples of milk, grouped into morning and evening samples, monthly samples for three consecutive years from the Institute herd, samples from Shorthorn, Guernsey, Ayrshire and Friesian cows, and other miscellaneous samples, has been determined. The mode for morning milk is 81–90 and for evening milk 71–80 mg. %. The mode for Guernsey and Shorthorn milk is 71–80 and for all (6076) samples, 81–90 mg. %. The mode for milk from herds of Friesians known to give milk of low content of solids-not-fat was 111–120 mg. %, but this must not be taken as the value for this breed generally. The average for Shorthorn milk is 97, Guernsey 93, Institute herd 93, all samples 98, special Friesian herd 128 and bulk Institute milk 85 mg. %.

Factors influencing the chloride content of milk such as breed, age of cow, lactation period, number of lactations, seasonal effects, and udder troubles have been discussed from inspection and by deduction from the series of values obtained.

The electrical conductivity of milk increases with chloride content but there is some deviation from the linear law. The conductivity increases at a greater rate than the chloride content in samples high in chloride, probably owing to the increase in electrolytes other than chloride.

1. The effect of commercial sterilization on the vitamin B complex, vitamin Bx and vitamin B2 (flavin) of milk has been investigated in experiments on rats using milk from the same bulk before and after heat treatment.

2. No quantitative comparisons were carried out regarding the vitamin B complex, but the tests showed that a considerable destruction of some component or components of it had been caused by the heat treatment and that vitamin B1 was, most probably, one of them.

3. Separate tests showed that about one-third of the vitamin B1 originally present in milk was destroyed by sterilization.

4. Sterilization appeared to have no adverse effect on vitamin B2 (flavin).

The accuracy of the casern number of milk as the basis for a chemical method for the detection of mastitis has been investigated. The number was determined for 247 samples of milk from the individual quarters of sixty-two cows, and the samples were examined bacteriologically for mastitis streptococci. Of the 247 quarters 49% were found to be infected—mostly subclinically—involving 74 % of the cows.

The total nitrogen content of the samples varied from 362· to 687·4 mg. per 100 ml., and the casein nitrogen from 153·0 to 554·0. The casein number varied from 42·3 to 83·4. The casein number averaged 79·2, 80·4, 79·5 and 80·3 in the samples from the uninfected quarters of the Shorthorn, Friesian, Ayrshire and Guernsey cows respectively; and 71·7, 74·1 and 70·3 in the samples from the infected quarters of the Shorthorn, Friesian and Ayrshire breeds respectively.

For the diagnosis of mastitis from the casein number, a figure of 78·0 and less was taken as indicating an infected quarter, and on comparing this chemical method with the bacteriological method, out of a total of 243 quarters, the chemical result differed from the bacteriological for 21 quarters—representing 8·6 % of the total.

Reasons are given for considering that this estimate of the error is excessive and that in practice the casein number would provide a valuable and rehable method for the diagnosis of mastitis.

Improved methods have been evolved for the separation of the total protein, casein, albumin, globulin, and proteose-peptone substances of milk.

I. The use of acetic acid-sodium acetate solutions for the precipitation of casein is elucidated, and it is shown that the maximum precipitation of casein is rapidly effected from milk samples of varying casein content by the addition to 10 ml. of milk of about 80 ml. of water at 40° C. and 1·0 ml. of 10% acetic acid solution, followed, after 10 min., by 1·0 ml. of N sodium acetate solution.

This maximum precipitation was found to be 1·0–1·4% greater than by Moir's method, and 2·4–3·8% greater than by the method of the Association of Oflicial Agricultural Chemists.

A procedure is suggested for the determination of casein which avoids the tedious transfer and washing of the precipitate, and gives enhanced ease, accuracy and speed of working.

II. The advantages of trichloroacetic acid for the precipitation of proteins in determinations of the total protein and the non-protein nitrogenous substances of milk are discussed.

The trichloroacetic acid methods at present in use are shown not to give complete precipitation, and for this a rapid method employing, at room temperature, a final concentration of 12% acid in the milk-acid mixture is recommended.

III. An accurate method for the precipitation of globulin uncontaminated with either albumin or casein is described.

IV. Methods are given for the precipitation and separation of the albumin and proteose-peptone substances.

It has been repeatedly pointed out(1, 2, 3) that the properties of cheese during the different stages of its manufacture should be correlated with the hydrogenion concentration rather than with the titratable acidity. Little systematic work has, however, so far been carried out in this direction, except for a study of the relationship between pH and titratable acidity in Cheddar cheese by Brown & Price(4). In planning work on similar lines, it was realized that the potentiometric methods of determining pH require expensive equipment and skilled attention, so that a supplementary colorimetric method, if sufficiently accurate to indicate the major changes in pH, should appeal more strongly to the practical cheesemaker on account of its cheapness and simplicity and the ease with which the outfit can be transported.

The solids-not-fat content (expressed as a percentage of fat-free milk) has been determined for 247 samples of milk from the individual quarters of sixty-two cows. The samples were also examined bacteriologically for the presence of mastitis streptococci and 121 were found to be infected, 114 uninfected, and twelve “doubtful”.

The solids-not-fat content of the uninfected samples varied from 8·24 to 10·28 and of the infected samples from 4·26 to 9·92. For the uninfected samples of the Shorthorn, Friesian, Ayrshire and Guernsey breeds it averaged 9·36, 9·11, 9·82 and 9·83 respectively, but in the infected samples only 8·44, 8·38, 8·28 and 9·49%.

Of the 247 samples, 36 % were below 8·80 in solids-not-fat content. Of 121 infected samples, 63% were below while of the 114 uninfected samples only 9% were below this standard. Hence 88% of the samples below 8·80 were infected samples, thus showing that subclinical mastitis accounts for a very high percentage of samples low in solids-not-fat content. In these samples the average value for solids-not-fat was 7·93%. The few uninfected samples that were low in solids-not-fat averaged 8·56%.

Measurements are reported of the solubility, in water and in sodium chloride solution of different concentrations, of the protein of cheese at various times after manufacture. The solubility in 3–10 % sodium chloride solutions reached approximately 100% within 7 days after manufacture of the cheese, both for normal and high rennet cheese, and remained at that value throughout the life of the cheese (8 months). Since the proteins of cheese are thus shown to be equally soluble in sodium chloride solutions corresponding in concentration to those encountered in the whole range of commercial cheese(1), the effect of salt concentration on cheese quality is not to be attributed to a variation in the solubility of the protein in the brine.

Details are given of a semi-micro Kjeldahl method for the determination of the total, casein, albumiij, globulin, proteose-peptone, and non-protein nitrogen of milk. The method is accurate, rapid, and particularly suitable for the determination of the smaller nitrogen fractions.

The various nitrogen fractions are separated by the improved procedures described in the preceding paper.