VII. \'ii'\Mi\ \ i)i;m('Ii;\(Y in \\im\i-s 107 



The iinpri'ssi\e clum^ivs in inoiplmlotiy and striKturc (,!' ti^■.su(■^ which 

 RMiiain viable, thoiijih protouiKlly alteicd in t'uiiction, suKS'^'^^t that the role 

 of vitamin A is somewhat in character ot a hormone or of an induclor 

 or evocator. Actually, the epithelial changes attending \itamin A deh- 

 ciency and recovery therefrom duplicate ac(nu-ately those of the vaginal epi- 

 thelium accompanying the estrous cycle of mammals. IIyper\'itaminosis 

 A bone effects, like the patterned growth of fetal hone, arc umelated to 

 concurrent functioning though conforming to normal growth patterns. In 

 general, the morphologic results of vitamin A deficiency are most pro- 

 nounced upon growth and differentiation of tissues — in growing and 

 adult animals by keratinization of epithelia which are renewed by mul- 

 tiplication of basal cells, in fetal life by many malformations, and in 

 early postnatal life by retardation of skeletal growth throughout the pe- 

 riod of growth. Skeletal growth may be retarded by deficiency of \-ita- 

 min A beyond the normal growth period of a species and be resumed 

 following vitamin A administration. 



Of interest is the fact that all \'ertebrates require an outside source of 

 vitamin A or a carotenoid preciu'sor, for vision, for maintenance of many 

 epithelia, andfor tooth and skeletal growth. This holds true for all animals 

 thus fai- tested — man, monkeys, pig, cattle, dog, fox, rabbit, guinea pig, 

 rat, mouse, fowl.^' - The hypervitaminosis A effects upon skeletal growth 

 have been observed in man, dog, guinea pig, rat, mouse, and fowl.^- ' 



B. VITAMIN A DEFICIENCY, POSTNATAL 



1. Epitheli.vl Tissues and Organs 



Epithelia of ectodermal, mesodermal, and entodermal origin are similarly 

 affected. The results summarized are: ati'ophy, reparative proliferation by 

 ba.sal cells, and growth and differentiation of the new cells into a stratified 

 keratinizing epithelium. The replacement epithelium, regardless of the origi- 

 nal function and structure of the region, is identical in all locations and 

 comparable in all its layers with epidermis.^- -• ^ Disregarding semantics, 

 for the sake of brevity I shall refer to the sequences which result in forma- 

 tion of the replacement epithelia as keratinizing metaplasia. The result of 

 repair induced by vitamin A administration is that, regardless of the identi- 

 cal composition of the replacement epithelium, theie is return to normal 

 in moi'phology and function for each region." 



' S. li. Wolhach. ./. Am. Med. Assoc. 108, 7 (Ifl.STi. 



- H. II. Follis. .Ii-.. The Pathology of .\ut ritional Di.scnsc. ( 'h.iilc.-^ (' Tiiomas, 



SpriiiKlicM. III.. 1948. 

 ' S.. B. Wolliach, ./. Biinr aii'l .foiiil Suni.. 29, 171 (l'.)47i. 



' C. L. Maddock. S. H. W.ill.adi. .in. I S. J. .Maddock. ./. Xulrilmn 39, ! 17 (I!)4()). 

 5 8. B. Woll)ach and (). .V. Bcsscy. I'h,js,,>l. h'vrs. 22. ZV.\ (l<M2i. 

 SS. B. Woll)acli and \\ \{. Howe, ./. AV/>//. Mol. 57, .511 (I'.KW). 



