598 IX. CAROTENOIDS AND VITAMINS A 



duced by withdrawing vitamin A from rats previously subjected to a diet 

 lacking in some of the heat- stable members of the vitamin B group. '"^'' 



f. Effect on the Teeth: A deficiency in vitamin A has an especially 

 severe effect upon the incisors of rats and of guinea pigs.'"^* These teeth 

 are growing continuously, and thus constantly rerjuire vitamin A for growth 

 processes. The main site of action of vitamin A is on the odontogenic 

 epithelium. In the absence of vitamin A, growth continues at the basal 

 formative end, but differentiation is incomplete. There is also a loss of the 

 organizing influence, and this results in an inadequate and defective den- 

 tine formation, and atrophic odontoblasts. The thinness of the dentine 

 layer causes it to assume an abnormal shape, and plication and buckling 

 of the dentine frequently occur near the formative end of the tooth. '"'^^ 

 The teeth of vitamin A-deficient animals present a thick dentine layer on 

 the labial side, and excessively thin layers elsewhere. Skaloud"*^^ re- 

 ported that the dental deterioration and malformation due to vitamin A 

 deficiency may be compensated for by the administration of vitamins C 

 and D. 



(6) Effect on the Bones. Although a deficiency of vitamin A does not 

 affect the structure of mature bones, it does have a profound effect upon 

 growing bones.'"-* Vitamin A deficiency presents a different type of re- 

 tardation of skeletal growth and interference with growth pattern than does 

 inanition or deficiency in other vitamins. For a description of the histo- 

 logic skeletal changes, the reader is referred to Wolbach.'^^^ When a 

 vitamin A deficiency exists, a retardation of skeletal growth may occur 

 without affecting that of the soft tissues of the nervous system.'"" How- 

 ever, according to Wolbach,'"^^ in vitamin A deficiency endochondral bone 

 growth ceases before the growth rate of the animal as a whole is seriously 

 affected. This results in disastrous imbalance between the development 

 of the skeleton and of the soft tissues in young animals. The cranial 

 cavity and spinal canal become too small for the central nervous system, 

 resulting in pressure upon the brain, spinal cord and nerve roots, with 

 consequent paralysis and other symptoms. Although the skeletal growth 

 of the human infant has not been studied in relation to vitamin A intake, 

 the results of studies on the rat, guinea pig, dog, duck, and chick are uni- 

 form in indicating a prompt cessation of epiphyseal growth in the absence 

 of vitamin A. Furthermore, all growth of the skeleton dependent upon re- 



1054 M. Sullivan and V. J. Evans, Arch. Dermatol and Syphilol., 51, 17-25 (1945). 



10^5 Y. Skaloud, Z. Vitaminforsch., 19, 2~M (1947). 



1056 S. B. Wolbach, /. Bone and Joint Surg., 29, 171-192 (1947). 



10" S. B. Wolbach and O. A. Bessey, Arch. Pathol, 32, 689-722 (1941). 



