XXVI CONTENTS 



IX. The Metabolism and Nutritional Value of the Carolenoids and 

 Vitamins A (continued) 



(2) Comparative Distribution of Carotenoids and of Vitamins A 



in Different Tissues 517 



(3) The Distribution of Carotenoids and of Vitamins A Witiiin tlie 



Cell 519 



(4) Factors Altering the Storage of Caroteoids and of Vitamins A. . . . 520 



a. The Effect of Age on the Storage of Vitamin A 520 



b. The Effect of Dosage on the Storage of Vitamin A 522 



c. The Effect of Sex on the Storage of Vitamin A 524 



(a) The Effect of Sex Hormones 525 



d. The Effect of Thyroid Function on the Storage of ViLaniin A 526 



e. The Effect of the Method of Administration on the Storage of 



Vitamin A 527 



f . The Effect of Tocopherols on Vitamin A Storage 527 



g. The Effect of Carcinogenic Drugs upon Vitamin A Storage ... 529 

 h. Miscellaneous Factors Affecting Vitamin A Storage 530 



7. The Metabolism of Carotenoids and of Vitamins A 534 



( 1 ) The Transformation to Vitamins A 534 



a. All-trans Carotenoids as Provitamins A 534 



(a) The Extent of Transformation of /3-Carotene to \'itaniiu A 538 



b. Cis-Trans Isomerization of Carotenoids, and Provitamin A 



Activity 540 



(2) The Transformation to Products Other Than Vitamin A 545 



(3) Vitamin A Analogues and Isomers 545 



a. The Relative Biopotencies of Vitamin Aj and Vitamin A2 545 



b. Cis-Trans Forms of Vitamin A and Their Biopotencies 547 



c. Other Compounds Active as Sources of Vitamin A 549 



(a) Vitamin A Acid 549 



(b) Vitamin A Aldehydes 549 



(c) Vitamin A Ethers 551 



(d) Vitamin A Hydrocarbon 552 



(e) Anhydrovitamin A (Ai) and Rehj^drovitamin A 552 



d. The Vitamin A-like Effect of Lard 553 



(4) The Excretion of Carotenoids and of Vitamin A in the Urine. . 554 



(5) The Secretion of Carotenoids and of Vitamin A into Milk 555 



a. The Carotenoids and Vitamin A in the Milk of Different Species 556 



b. The Effect of the Lactation Cycle on the Carotenoids and Vita- 



min A in Milk 558 



c. Seasonal Variations in the Carotenoid and Vitamin A Content 



of Milk 559 



d. The Effect of Diet on the Carotenoids and Vitamin A in Milk. 560 



e. The Effect of the Thyroid Gland upon the Carotenoids and Vita- 



min A in Milk 562 



(6) The Secretion of Carotenoids and of Vitamin A into Eggs 562 



a. The Effect of Incubation on the Carotenoids and Vitamin A 



in Eggs 567 



(7) Antivitamin A 567 



