The preparation of crystalline rennin previously described (1) was somewhat long and inconvenient, but the knowledge gained about the properties of the crystals suggested that a simpler method might be successful. Since then Møgensen (2) has shown that the mere precipitation of commercial rennet with saturated sodium chloride gives a product with proteolytic properties resembling those of the crystalline material, and with enhanced milk-clotting activity per unit of dry weight. Some years previously, Hankinson (3) had also achieved considerable purification by these means. The results of an attempt to discover a simple method of crystallization are described below.

1. Some questions concerning the interpretation of observations on milking dairy cattle are considered.

2. A formula is presented for analysing the contributions of changes in the numerator and denominator to the changes in a percentage or fraction, and the formula is applied to changes in the composition of milk.

3. The depressions of the butterfat and solids-not-fat percentages consequent on diets reduced in hay in a dairy-cattle feeding experiment are examined with this constituent analysis.

The contributions of changes in the magnitudes of the aqueous, butterfat and solids-not-fat constituents to the difference between the butterfat percentages of cows on two treatments, 18 lb. hay/day (control) and 6 lb. hay /day, are about equal. There is an apparent qualitative difference between the effects of the two non-control treatments, and a reduced yield of butterfat would alone largely account for the lower butterfat percentage of cows on the 2 lb. hay /day treatment.

1. An investigation was carried out, using objectively measurable stimuli, to examine the method of assessing the size of the mammary glands of calves by palpation. The method was that described by Swett.

2. The results indicate that the estimated sizes may be very different from the true sizes, although the two are generally highly correlated. In most cases the estimated sizes are significantly smaller than the true sizes.

3. Different judges give very different estimated sizes for the same true sizes, thus it is not justifiable to compare directly glands which have been stated to be of the same size by different judges.

The milk-ejecting activity of the hormones of the posterior-pituitary gland is well known and has been adequately reviewed (1). Most of the published information deals with the lactating dairy cow. In the course of work at this Station involving the lactating sow as a basis for assay of the milk-ejecting hormones (2, 3), data have been collected on the effect of a standard dose of oxytocin. Our normal assay procedure (2) involves giving the animal a preliminary dose of 0·5 unit of oxytocin. Thus over one lactation we have been able to record the time between injection into the ear vein and the onset of milk let-down, and the period during which milk may be obtained by simple hand-milking, for a number of sows. Braude & Mitchell (4) have published figures for the milk let-down effects of doses of oxytocin ranging from 1 to 10 units. The following results were obtained with &5 unit. All sows used were of the Berkshire breed.

An analysis has been carried out on the milk yield, milk composition and milking-rate records collected in one herd of dairy cows.

It has been shown from the results of eighty-six heifers that for each pound per minute increase in inherent milking rate (i.e. peak flow) the standard lactation yield increases by 419 lb., the maximum daily yield by 0·9 lb., the lactation length by 8 days and the persistency index by 10 days, whilst the lactation solids-not-fat percentage decreases by 0·03 and the fat percentage by 0·04. All except the last coefficient were significant, although it was also shown that the relationship with solids-not-fat percentage was due to an interaction. Similarly, by the calculation of partial regression coefficients it was demonstrated that the relationship between milking rate and standard lactation yield was due to the effect of milking rate on maximum daily yield, lactation length and persistency.

1. Using the capillary technique previously described, examination has been made of various factors in relation to the reactivation of raw milk phosphatase. Of these, ageing of the raw milk was found to affect considerably the level of reactivation, this increasing as the bacteriological quality of the milk deteriorated.

2. It has been found that absence of air and the presence of reducing conditions in the raw milk increases the reactivation obtained.

3. The influence of reducing conditions on the reactivation of a bacterial phosphatase has been demonstrated.

Chemical factors reputed to promote fishiness in butter were studied. Attempts were made to reproduce fishiness in experimental churnings of butter by deliberately applying factors reputed to cause the defect, viz. low pH, high salt content, lack of pasteurization, traces of copper, borates—singly and in combination.

Eleven Shorthorn cows were milked for 14 days before their expected calving date. The total amount of prepartum secretion varied, between cows, from 1 to 961.

Determinations of total solids, fat, solids-not-fat, lactose, total protein, ash, calcium, phosphorus, chloride, casein, albumin, globulin, proteose-peptone, N.P.N., vitamin A and carotenoids were made regularly on the secretions of eight of these cows during the prepartum period, and for 4 days postpartum; and, for comparison, on five samples of Short-horn colostrum each representing the total secretion obtained from the two milkings within the first 24 hr. after calving.

The various theories commonly used to explain the increasing fat content of cow's milk with stage of milking are examined and found inadequate. It is suggested that the trends in fat content as a cow is being milked may be explained by the clustering of the fat globules and the consequent partial filtering out of the clusters as the milk flows from the gland. Evidence for clustering of fat in cow's milk at body temperature is presented and the application of the theory to the sow discussed.

The main types of surface milk coolers were tested using water at 95°F. instead of milk The coolers were tested: (a) for cooling efficiency at the nominal rated flow and a range of cooling-water flows; (b) for allowable flow at 3:1 cooling-water and cooling to within 3° F. of the cooling-water; (c) for the allowable flow (lb./hr. per square foot of cooling surface) for a range of cooling-water flows; (d) for the cooling-water pressures for various rates of flow.

The results showed that no cooler reached the required efficiency at a cooling-water ratio of 3:1 or less, the temperature difference at the bottom of the cooler varying from 3·3 to 7° F. for normal coolers.

The allowable flow per square foot of cooling surface varied from 33·8 to 114 lb./hr. when cooling to 3° F. difference with 3:1 water. The corrugated plate design had higher allowable capacity at low rates of flow of cooling·water than the tubular designs. Atmospheric cooling was small.

Some few months ago the National Agricultural Advisory Service, South West Sub-Centre, encountered several farms in their area where failure to reach the required standard for designated milk appeared to be connected in some way with pronounced pitting corrosion of aluminium alloy milking buckets, and, on the suggestion of Dr A. R. T. Mattick of the National Institute for Research in Dairying, Reading, the authors of this note were given the opportunity of examining a corroded pail and of tracing the source of the corrosion, if possible.

It has been found that when three strains of Bacillus cereus are grown in turn with each of two strains of Streptococci lactis and two strains of the coli-aerogenes group, the growth of the spore-formers is neither suppressed nor stimulated. It has been confirmed, however, that the spore-former is unlikely to develop if the milk is held at 15°C. or below. Broken cream results if marked growth of B. cereus occurs. A nisin-producing strain of Str. lactis did not retard the development of the spore-former in milk, but after initial increase the numbers of B. cereus decreased. Broken cream was not prevented.

Several media previously recommended for lactobacilli by other workers have been examined, but none was found to support good growth of all species. Experiments are described in which the optimum concentrations and combinations of various ingredients, particularly Tween 80, were determined. These resulted in the development of a practical medium which has proved satisfactory for the growth of all varieties of lactobacilli.

1. The numbers and species of micro-organisms surviving in commercial high-temperature short-time pasteurized milks sampled direct from the cooling section of the pasteurizer have been determined and compared with those in the corresponding raw milk and in the raw milk after low-temperature pasteurization in the laboratory.

2. The geometric mean counts at 37° C. for twenty-five samples of raw, L.T. and H.T.S.T. pasteurized milks were 74,130, 1,740 and 3,200 per ml. respectively. The corresponding figures at 30° C. were 123,030, 7,080 and 8,510 per ml.

3. The percentage destruction of the bacteria was slightly smaller at all four plants for the H.T.S.T. pasteurized milks than for the corresponding L.T. pasteurized milks. The mean percentage destruction for the L.T. pasteurized milks was 97·7% for bacteria growing at 37° C. and 94·3% for bacteria growing at 30° C. The corresponding figures for the H.T.S.T. pasteurized milks were 95·9 and 93·1%.

1. Iodinated casein or L-thyroxine, under the conditions of this experiment, had no adverse effect on the general health of a dual purpose (Red Poll) or a dairy breed (Ayrshire) of cattle.

2. The treatment did not increase the total milk or butter-fat production.

3. The treated animals did significantly better than the controls in one lactation only and in the following variables only: (a) daily milk yield adjusted for pre-treatment differences—Red Polls, lact. 1; (b) milk yield for duration of treatment adjusted for pre-treatment differences—Red Polls, lact. 1.

A number of strains of streptococci falling into serological group N which could not be identified as either Streptococcus lactis or Str. cremoris were isolated during a study of the bacterial flora of raw milk (1). These organisms were dominant in milk incubated at 22°C. until the end-point of the clot-on-boiling test in three out of the twelve samples examined and, apparently, had played a major part in their spoilage. Similar strains were isolated in smaller numbers from the samples aged under other temperature conditions.

1. Commercial samples of milk of Swiss origin, sterilized by rapid heating to high temperatures, developed a positive phosphatase reaction on storage.

2. The optimum temperatures of storage for the development of this positive phosphatase reaction was 30° C.

3. These commercial samples were sterile when received and remained sterile during storage.

4. The developed phosphatase is apparently identical with the normal alkaline phosphatase of raw milk as judged by (a) heat stability, (b) pH optimum and rate of hydrolysis at different pHs, (c) comparison of results by Kay-Graham and Aschaffenburg & Mullen tests.

1. A study has been presented of the machine milking rate of 141 cows recorded in 326 lactations.

2. The coefficients of variation between cows of various measures of machine milking rate are usually in the range 30–40%, whilst the within-cow variations are of the order of 8–11%.

3. The differences between the milking rates of cows in a single herd are given, together with the distribution of these differences.

4. Milking rate declines as lactation advances, the decline being greater for fast milking cows.

5. Lactation decline in milking rate is related independently to change in milk yield and to interval since calving.

An improved milk-flow recording instrument is described which is completely controlled by the milking operations in an experimental dairy and which automatically indicates the end of milking in terms of a predetermined rate of milk flow. The instrument makes possible the recording of milk-ejection curves without changing the milking routine or requiring an additional operator in the milking shed.

1. A diffusion cup technique using Micrococcus lysodeikticus has been found suitable for lysozyme estimation. By this method raw milk gave only small zones of inhibition. The inhibitory substance of milk was shown not to be lysozyme.

2. Dose-response curves (dilution v. pH) were obtained with Streptococcus pyogenes as the test organism. They indicated that the effect of milk on this organism was the result of the interaction of one stimulatory and at least two inhibitory substances.

3. The existence of two inhibitory substances was confirmed by dilution assays, one, L1, occurring mainly in colostrum, the other, L2, occurring mainly in milk. The inhibition is greatest when L1 and L2 act simultaneously.

4. The pH and heat stabilities of the two substances are slightly different. L1 is most stable at pH 6−6·5, 90% being destroyed at 68° C. L2 is most stable at pH 7 and 95% is destroyed at 74°C.