LIPIDS PRESENT IN MILK FAT 797 



of the Boer group were not confirmed by von Euler et al. m - m The Dutch 

 workers explain this discrepancy by the possibility that the butter employed 

 by the Swedish investigators did not contain vaccenic acid, since it was not 

 summer butter. However, negative results as to the growth-stimulating 

 effect of vaccenic acid have been reported by a number of workers, 504-506 

 including the latest communication of Boer ei aZ. 507 If such a seasonal 

 variation in milk composition does actually exist insofar as vaccenic acid 

 is concerned, it probably has a dietary origin. Variations in the proportion 

 of the carotenoids and vitamin A in milk, which are likewise seasonal, are 

 the result of differences in the content of these components in the feed. 



Although seasonal variations in the composition of milk fat can be largely 

 ascribed to the indirect effect of season on the food available to the cows, 

 Ragsdale and Brody 508 stated that low environmental temperature is the 

 direct cause of an increased fat level in cow's milk. This is in line with a 

 comprehensive study by Ragsdale and Turner 509 on the fat content of 

 different breeds. It was shown that the lowest levels of fat obtained in the 

 summer and the highest content occurred in the winter. These latter 

 workers reported that low temperatures per se were the cause of high fat 

 content. 



d. The Effect of Hormones on Milk Fat. The most important hormone 

 related to milk production is that secreted by the anterior lobe of the pitui- 

 tary gland; it has been called prolactin, luteotropin, or simply the lactogenic 

 hormone. It is a protein, slightly soluble in water, having an isoelectric 

 point of 5.5, and a molecular weight of about 30,000. Preparations of the 

 hormone from the pituitaries of sheep and cattle cannot be differentiated 

 electrophoretically; presumably they are identical. The pure hormone 

 has been prepared by a number of investigators. 510 " 513 An excellent re- 



602 B. von Euler, H. von Euler, and I. Saberg, Ernahrung, 7, 65-74 (1942). 



603 B. von Euler, H. von Euler, and I. Saberg, Ernahrung, 8, 257-264 (1943); Chem. 

 Abst., 39, 4921-4922 (1945). 



604 H. J. Deuel, Jr., S. M. Greenberg, E. E. Straub, D. Jue, C. M. Gooding, and C. F. 

 Brown, /. Nutrition, 35, 301-314 (1948). 



605 H. Nath, V. H. Barki, C. A. Elvehjem, and E. B. Hart, J. Nutrition, 36, 761-772 

 (1948). 



806 B. von Euler, H. von Euler, and G. Lindeman, Ark. Kemi Mineral., Geol., 26B, 

 No. 3, 1-5 (1948). 



607 J. Boer, E. H. Groot, and B. C. P. Jansen. Voeding, 9, 60-62 (1948); Chem. Abst., 

 42, 7847 (1948). 



608 A. C. Ragsdale and S. Brody, J. Dairy Sci., 5, 212-215 (1922). 



609 A. C. Ragsdale and C. W. Turner, J. Dairy Sci., 5, 544-554 (1922). 



610 C. H. Li and H. M. Evans, "Chemistry of Anterior Pituitary Hormones," in G. 

 Pincus and K. V. Thimann, The Hormones, Vol. I, Academic Press, New York, 1948, 

 p. 648. 



611 A. White, Ann. New York Acad. Sci., 43, 341-381 (1943). 



612 A. White, Vitamins and Hormones, 7, 253-292 (1949). 



613 W. E. Petersen, Recent Advances in Hormone Research, 2, 133-158 (1948). 



