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.