CONTENTS XXVll 



fX. The IMolabolism aii«l Niilrilional \ alue of llir CaroUMioids and 

 ^ itaniiiis A (continued) 



8. The Importance of Carot.cnoids and ol' Vit;Mniii8 A in Vision 568 



(1) Biochemical Systems Involved in Vision in Higher Animals 569 



a. Retinal Pigments 569 



(a) Rhodopsin 569 



(b) Porphyropsin 569 



(c) lodopsin 570 



b. Vitamin A Aldehj^de 570 



(a) Vitamin Ai Aldehyde (Retinenei) 570 



(b) Vitamin A2 Aldehyde (Retinene2) 570 



c. The Alcohol Dehydrogenase System 570 



(2) The Synthesis of Rhodopsin in Higher Animals 571 



a. The Synthesis of Rhodopsin from Retinene 571 



1). The Synthesis of Rhodopsin from Vitamin A 571 



(a) Neo-6 Retinene as a Required Precm-sor 573 



(3) Species Variations in Biochemical Requirements for Vision 575 



9. The Requirements of Animals for Carotenoids and for Vitamins A. . . . 576 



( 1 ) Introduction 576 



(2) Factors Altering the Requirement for /3-Carotene and for 



Vitamin A 578 



a. Species 578 



(a) Rat 579 



(b) Mouse 581 



(c) Guinea Pig 581 



(d) Rabbit 582 



(e) Dog 582 



(f) Chickens, Turkeys, and Other Fowl 582 



(g) Swine 585 



(h) Cattle 585 



(i) Sheep 587 



(j) Horse 587 



(k) Other Animals 587 



(1) Man 588 



b. Sex 589 



c. The Administration in Aqueous Dispersions 589 



d. The Form of Vitamin A 589 



e. Stress Factors 590 



f. Dietary Components Fed Simultaneously 591 



(a) Tocopherols 591 



(b) Vitamin Br. 592 



(c) Proteins 592 



(d) Choline 592 



(e) Antibiotics 592 



(f) Mineral Oil 592 



10. Hypovitaminosis A (Avitaminosis A) 593 



( 1 ) Introduction 593 



(2) Deficiency Symptoms in Animals Other Than Man. , , 594 



