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IN previous communications [Booth et al., 1933, 1, 2], the seasonal variations in the carotene and vitamin A contents of the butter fat produced from typical English milk were described, and a seasonal variation in the power of butter fat to inhibit the reaction between vitamin A and antimony trichloride was established. We also mentioned that the fatty acids prepared from summer and winter butter fats appeared to show certain differences, namely (1) acids from summer butter fats showed more intense absorption at 230m,u than those from winter butter fats, and (2) summer acids turned brown more rapidly than winter acids when treated with the antimony trichloride reagent. It was not clear at the time whether or not these two properties were related to the greater inhibitory power of summer butter fat in the antimony trichloride test. Further work has now demonstrated that neither the 230m,u absorption nor the rate of brown colour formation can be correlated with the inhibitory power. The rate of brown colour formation, indeed, is greatly increased in aged or oxidised fats, and any decision as to whether a seasonal variation of this property does actually exist must be postponed until one is in a better position to understand the nature of the reaction involved. On the other hand we have satisfied ourselves that the variation in absorption at 230m,u is of a genuinely seasonal character. Data in support of this view are given below. EXPERIMENTAL.

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