Connecting the trend of the different parts of the lactation curve with what is believed to be the underlying hormonal mechanism, it has been pointed out that any analysis of the curve must deal separately with three parts. The central portion, lying between the peak of daily production and the rapid decline (drying off) has been the object of investigations in an inbred Ayrshire herd. Coefficients of persistency were obtained by fitting exponential curves to this central portion. When first lactations were excluded and correction for month of calving applied, the coefficients (P) were found to be reasonably consistent for different lactations of the same cow. Month of calving accounted in this herd for about one-third of the variance of P. Of the remaining variance approximately one-half is attributed to differences among cows. A possible physiological explanation of the cause of the well-known negative correlation between maximum yield and persistency has been suggested. No conclusions can be drawn from this material on the relative importance of heredity and environment in determining persistency.

1. In a large-scale experiment, using about 500 cows, half the cows were fed a production ration consisting of decorticated ground-nut cake, maize meal, wheat offals and molasses supplying about 0.6 lb. protein equivalent per 10 lb. milk produced, and the remaining half were fed a production ration containing the same constituent foods in different proportions supplying a similar starch equivalent, but only two-thirds the amount of protein. No measurable difference was observed in the fatness, handling properties of the skin, hair on the body and percentage of fat and solids-not-fat in the milk.

The milk yields showed no difference during the winter feeding period of about 20 weeks, but during the succeeding period when all the cows were allowed ample grass the milk yield response of the cows previously given the low-protein ration was significantly greater than that of the corresponding cows previously given the high-protein ration.

The experiment was repeated the following winter, using about 600 cows, and confirmatory results were obtained.

2. Another experiment similarly planned, using 300 cows, compared highwith low-protein production rations consisting of the constituents noted above together with soya-bean meal and rice bran. No significant differences were observed between the effect of the two rations on milk yield or composition, fatness of the cows, etc. There was, however, an indication (not statistically significant) that the low-protein ration which contained a relatively high proportion of rice bran depressed the milkfat percentage.

3. A small but more completely controlled experiment confirmed the findings of the large-scale experiments.

1. The influence of temperature, oxygen tension, yeast autolysate and chalk on the production of by-products and the ratios of by-products formed to sugar utilized and lactic acid produced in milk by the lactobacilli has been investigated.

2. The total production of lactic acid is increased by the presence of chalk and “growth factors” but is not affected by temperature or oxygen tension. The ratio of lactic acid produced to sugar utilized is decreased at lower temperatures and increased by chalk but yeast autolysate and variation in oxygen tension give variable results.

3. The total production of acetic acid is increased by the presence of chalk, and “growth factors” and by anaerobic conditions. The ratios of acetic acid produced to sugar utilized and lactic acid formed are decreased by chalk and anaerobic conditions and there is a tendency for the ratios to be decreased by the presence of yeast and increased at lower temperatures.

4. The total production of alcohol is increased by anaerobiosis and also by the presence of chalk and yeast in the medium. The ratios of alcohol formed to sugar utilized and lactic acid produced is increased by anaerobic conditions, and chalk also tends to increase the relative amount of alcohol. Temperature and yeast autolysate have little effect.

5. Chalk is effective in maintaining the pH at a higher level during growth, but the influence of chalk on the ratios of by-products formed to sugar utilized is probably not entirely a pS. effect since the addition of talc to the medium has an equally strong influence in altering the relative production of lactic acid and alcohol.

6. It was previously shown for the heterofermentative streptococci that the Pasteur effect (suppression of alcoholic fermentation by respiration) is slight; similar results have been obtained with the heterofermentative lactobacilli.

Part I

1. A method for the estimation of vitamin B1 in milk by a modified Jansen test involving takaphosphatase treatment is described in detail.

Part II

2. It is shown by ultra-filtration experiments, by treatment with pepsin and takaphosphatase, with trichloroacetic acid and with fuller's earth that vitamin Bx is present in milk unesterified and phosphorylated and that both forms may be freely diffusible or combined with protein either loosely or by firmer bonds.

Part III

3. The effect of the stage of lactation on the amounts and partition of vitamin B1 in milk has been studied. Samples of colostrum and early milk were found to contain large amounts of cocarboxylase (up to 80 % of the total). Hardly any cocarboxylase was present in mid or late lactation milks. The total vitamin B1 content was 60–100μg./100 ml. for colostrum, up to 60μg./100 ml. for early milk and 30–40μg./100 ml. for mid and late lactation.

4. A marked negative correlation exists between the cocarboxylase content of cow's and goat's milk and their alkaline phosphomonoesterase titre. As this enzyme cannot dephosphorylate cocarboxylase it is probably accompanied in milk by other enzymes more suited to this process.

5. The suggestion is put forward that the vitamin B1 of milk is mostly derived not directly from the blood but from the secretory cells of the mammary gland.

Since publication (1) the apparatus previously described by the authors has been altered and improved. The alterations have been concerned mainly with excluding draughts and securing a better form of support. In using the apparatus we have found that the absence of vibration is important for the agreement of duplicates. It would seem that vibration tends to break the cohesion between the curd and the surface of cylinder A. For this reason a part of the laboratory as free as possible from vibrational disturbances was chosen and the support fixed to the wall.

1. A method is described for measuring the consistency of cheese curd during the scalding process which has been found satisfactory with Cheddar, Cheshire, Leicester, Double Gloucester, Caerphilly, Kingston and Derby cheese and is probably applicable to some other varieties.

2. The property (W/h), taken as a criterion of consistency, can be measured within less than 1 min. and is highly correlated with moisture content except when abnormal scalding conditions produce an uneven distribution of moisture in the curd. The size of cut does not affect this correlation within wide limits, though both moisture content and W/h are regularly affected by size of cut until the curd is approximately ready to pitch, at which point both properties show unique values independent of size of cut.

3. When the curd is nearing the pitching point, W/h measures the extent to which a standard cylinder of curd loses whey, the liquid being replaced in the solid structure by air. At an earlier stage in the scalding process the capacity of the curd to retain its shape under the force of gravity also affects W/h.

4. Although the cheese-maker judges the consistency of curd suitable for pitching by a complex mixture of properties, it is believed that Wjh will serve as an effective single-value criterion of consistency, suitable for judging pitching time if the acidity is also known.