COMPOSITION AND FOOD VALUE OF BUTTER 17 



is a higher temperature and more prolonged period of heat- 

 ing than the milk-fat is subjected to during the process 

 of manufacture into butter. The growth-promoting sub- 

 stance seems to be in greatest quantity in milk-fat. In 

 comparison with beef-fat, the growth produced by milk- 

 fat was more marked and more prolonged.^ In both, the 

 factor efficient in facilitating growth is found in the fats 

 with Ibw melting points.^ 



13. eomparison of butter and margarine. — As a food 

 for growth, butter is superior to the best grades of marga- 

 rine that contain some beef and to the margarine that con- 

 tains no beef; for there is no fat-soluble A and water- 

 soluble B in the margarine that contains no milk-fat nor 

 beef-fat. Even in the margarine that contains milk-fat 

 or beef-fat, the growth-promoting substance is so small that 

 its value cannot be compared with that of butter. McCol- 

 lum ^ says : " Experiments which we conducted a year ago . 

 show that 3 per cent of butter-fat furnishes the minimum 

 supply of this factor for normal growth in young rats. In 

 comparable experiments 10 per cent oleo was the minimum 

 which would serve this purpose." The factor to which 

 McCollum refers is " fat-soluble A substance." This 

 shows that butter contains more than three times the 

 quantity of this vital substance than is found in margarine. 



^ Osborne, T. B., and Mendel, L. B., Further Observations of 

 the Influence of Natural Fats upon Growth, The Jour. Biol. 

 Chem., Vol. 20, pp. 37 and 384, 1915. 



2 McCollum, E. v.. The Relative Nutritive Value of Oleo- 

 margarine and Butter, Univ. Wis., Jour. Home Boon., p. 229, 

 1917. 



