CONTENTS XXIX 



X. The Metabolism and Nutritional Value of the \ itaiiiins U 621 



1. Introduction 621 



(1) Rickets 621 



(2) Tlie Provitamins D 62^ 



a. Structural Requirements for Activity 623 



b. Occurrence of Provitamins D in General 628 



c. Occurrence of Specific Provitamins D 629 



(a) Ergosterol 629 



(b) 7-Dehydrocholesterol 635 



(c) Miscellaneous Provitamins D 635 



(3) The Vitamins D 636 



a. General Structural Requirements for the Vitamins D 637 



b. Production of the Vitamins D from the Provitamins D 639 



c. Occurrence of the Vitamins D 641 



(a) Vitamins D in Fish Oils 643 



(b) Vitamins D in Higher Animals 648 



2. The Digestion, Absorption, and Transport of the Vitamins D 651 



(1) The Absorption of the Vitamins D 651 



(2) The Transport of the Vitamins D 654 



3. The Further Metabolism of the Vitamins D in the Tissues 655 



4. The in vivo Activation of the Provitamins D 657 



5. The Effect of the Vitamins D on Various Physiologic Processes 658 



( 1 ) Introduction 658 



(2) The Absorption of Calcium and Phosphate 659 



a. Balance Experiments on Calcium and Phosphate Metabolism 



in Rachitic Infants without and with Vitamin D 659 



b. Vitamins D in Relation to Calcium and Phosphate Metabolism 



in Species Other Than Man 662 



c. On the Mechanism of Action of the Vitamins D on Calcium and 



Phosphate Balances 663 



(3) The Effect on Phosphate Metabolism 665 



a. Vitamin D and Phosphate Resorption in the Kidnej^s 667 



b. Phytic Acid and the Action of Vitamin D 668 



c. Phytase and the Action of Vitamin D 669 



(4) The Action on Bone Formation 670 



a. As Related to Citrate Content 671 



(5) Vitamin D and the Formation of Teeth. . . 672 



C6) Vitamin D in Relation to the Intestinal and Fecal pH 673 



(7) Vitamin D and Respiratory Metabolism 674 



6. The Requirement for Vitamins D 675 



(1 ) In the Lower Animals 675 



a. Chickens and Poultry 675 



b. Swine and Dairy Cattle 677 



c. Other Species 677 



(2) In Man ^^___. 678 



7. H,\'pervitaminosis D /^^xCiJ C/^ /^*\^ 678 



( 1 ) Symptoms of Hypervitaminosis D . . ■/^^j^'S^c^'J;sjC&\ ^"^^ 



