An investigation of the milk of a typical herd of Shorthorn cows kept under south of England conditions has been carried out.The results of the first three years of the investigation are now recorded. The plan of the experiment, the history of the cows during the period, the management, feeding, milking, and milk yields are described and illustrated in Tables I and II.

A GREAT deal has been written during the last few years upon the effects-deleterious or otherwise-of heat upon milk. That certain changes are brought about in the composition of milk by heating seems to be generally agreed, but enquiries into the nature of these changes have generally been made only at one or two particular temperatures. It was felt that possibly results of more value might be obtained by studying the effect of heating milk over a wide range of temperature, and it was decided to investigate the effect of heat upon [a) the time of coagulation by rennet, and (b) the solubility of the calcium, phosphorus and nitrogen present.One of the most fundamental properties of milk is its coagulability by rennet and in the manufacture of cheese the production of a satisfactory curd from the milk on the addition of rennet is one of the most important factors. Upon the nature of the coagulum formed in the early stages of the manufacture of any cheese depends to a great extent the quality of the final product. For the production of a good cheese, it is necessary that a firm coagulum shall be produced by the addition of a definite quantity of rennet to a known volume of milk at a standard temperature. If for any reason, coagulation is delayed, and the resulting coagulum is soft, whey will not drain freely from the curd, and the resulting product will generally be poor both in texture and flavour.In practice it has been found by cheese makers that a soft unsatisfactory curd which is difficult to drain is always produced when the usual quantity of rennet is added to milk which has been pasteurised, but it has also been found that the addition of lime water or a solution of caWium chloride to the milk before the addition of rennet results in

This paper contains the results obtained in the fourth and fifth, years of a study of the milk of a typical herd of healthy Shorthorn cows. The period of drought in the summer of 1933 is included and furnishes analyses which differ so much from the four previous years that the daily figures are given in Chart 1. In the earlier paper (i) weekly averages only could be published. The greatest seasonal variations which have been demonstrated by the daily analyses are:(1) A fall of the percentage of fat in the morning's milk in the spring when the cows were on young grass. This was clearly shown in each of the five years.(2) A fall in the percentage of solids-not-fat in the evening's and morning's milk during the period of drought in 1933, to an extent which had not previously been recorded.The causes of these changes in the composition of milk will be further studied using the milk of individual cows.The weekly analyses of morning's milk have also shown seasonal variations.Relatively high values of the titratable acidity, formol titration, ash, calcium and phosphorus were observed from October 1931 to February 1932, followed by a general decrease in the summer months, while in the late autumn somewhat higher values were again found.During the summer and early autumn of 1933 values which were lower than any previously obtained during this investigation were recorded for formol titration and for phosphorus, while the time of coagulation with rennet was longer.Preliminary consideration of the data has revealed the possibility that the fall in non-fatty solids may be particularly associated with the phosphorus content.

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An enzyme which hydrolyses tributyrin is present in all samples of fresh cows' milk examined. A method has been developed for the determination of the tributyrinase activity of a given milk or fluid.In milk the enzyme is present in the aqueous rather than the fatty portion. Its optimal range of activity is in the region pH 8·2–8·7. It is rather more thermolabile than phosphatase.Its concentration in milk varies considerably from cow to cow, and in individual healthy cows there is a fairly regular variation throughout the lactation cycle. It is highest in concentration in colostrum, then the concentration falls to a minimum at about 10 days, rising later to a figure intermediate between this minimum and the colostral value. It shows no sign of increase towards the end of the lactation period.Its relationship to the “true lipase” of milk is discussed.