The relation of the colour and vitamin A content of butter to the nature of the ration fed

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Synapse has enriched 4 closely related papers on similar clinical questions. Consider them for comparative context:

1. 1Characteristics of highly active vitamin A preparations1932 · 56 citations
2. 2Variations in the quality of butter, particularly in relation to the vitamin A, carotene and xanthophyll content as influenced by feeding artificially dried grass to stall-fed cattle1933 · 40 citations
3. 3A study of seasonal variation in butter-fat1933 · 47 citations
4. 4The use of 7-methylindole in the antimony trichloride colour test for vitamin A1932 · 22 citations