SECTIONAL TRANSACTIONS.—B. 301 
several fractions that differ in chemical composition, especially in their 
content of phosphorus. Mixing the fractions in their original proportions 
gives the original casein with its characteristic physical and chemical 
properties. 
Investigations of the solubility of casein in acids and bases show its 
complex nature. The solubility is, under constant conditions, a function 
of the amount of casein present as precipitate, and the dissolved substances 
differ in chemical compositions from the precipitate. 
The fact that casein is a mixture makes investigations of its chemical 
structure difficult. Due to its high content of phosphorus and the 
importance of this to nutrition problems, the mode of combination of this 
element has been the subject for elaborate studies. Experiments show that 
the phosphorus in casein is present as phosphoric acid and—at least partly 
—bound to serine by an ester linkage. As the phosphorus content of the 
different fractions of casein is different, this problem is of importance to 
the explanation of the above-named physical properties. 
Prof. T. P. Hitp1rcu.—The chemical nature of the glycerides of milk- 
fat (11.50). 
The methods available for the rapid characterisation and routine analysis 
of milk-fats are insufficient to give detailed information as to the fatty acids 
and glycerides present therein. The present knowledge of milk-fat acids 
and glycerides and of the procedures adopted in their study are briefly 
summarised. ‘The available data permit some comparisons to be made 
between the milk-fats of cows and of other animals, and also suggest some 
of the ways in which the milk-fat components may be varied as a result of 
change in the diet of the animal, in its age, or in certain other factors. 
Certain acids (e.g. butyric, caproic, palmitic, stearic, oleic) are present in 
important proportions in milk-fats, whilst others (some of which may be 
peculiar to milk-fats) are present in minute proportions. ‘The recent 
work of Brown and others on some of the latter acids is described. 
There is at the moment some uncertainty as to the presence of linoleic 
or other polyethenoid acids of the C,, series in butter fat, and this subject is 
discussed in the light of recent work. 
Dr. S. K. Kon.—The vitamins of milk (12.10). 
A study of the vitamin content of milk produced under conditions typical 
of the South of England practice has been in progress for the last three years 
at the National Institute for Research in Dairying, Reading. Biological 
tests have demonstrated marked seasonal variations in the total vitamin A 
activity and in the vitamin D content of milk. Physical measurements show 
a similar fluctuation in the carotene content. ‘The concentrations of the 
vitamin B complex, vitamin B, and vitamin B, appear to be constant through- 
out the year and are not affected by the season. ‘The amounts of vitamin A, 
B, and D present in milk at different seasons of the year are given in terms 
of the respective International Standards. 
It has been shown in joint work with Drs. Moore and Dann of Cambridge 
that the SbCl, test for vitamin A cannot be applied directly to butter owing 
to the presence in the latter of an inhibitor showing seasonal variation. The 
inhibitor is removed by saponification. The total vitamin A activities of 
Shorthorn and Guernsey butters produced under identical conditions of 
feeding and management are equal. On the other hand, Shorthorn butter 
contains more vitamin A and less carotene than a corresponding Guernsey 
