596 IX. CAROTENOIDS AND VITAMINS A 



ments of the rod occurred, the correction of which required longer periods 

 of vitamin A therapy. When the lesions involved the greater part of the 

 outer nuclear layer, the damage became irreparable, even when vitamin A 

 was given. 



In addition to the changes in the retina, the epithelia of the cornea and 

 the bulbar and palpebral conjunctivae become keratinized.^"-* Concur- 

 rently with the epithelial changes in the cornea, blood vessels grow into 

 the tunica propria from the limbic plexus. The ducts of the lacrimal glands 

 undergo keratinization, and the glands themselves become atrophied. 

 Xerophthalmia results when these keratinized cells accumulate in the con- 

 jmictival sacs and excite inflammatory reactions. Keratomalacia, which 

 entails edema and necrosis of the cornea, may occur. Bacterial invasion 

 is favored by the accumulation of keratinized cells, and this may result in 

 ulceration of the cornea and hypopyon. ^"^^ The gross ocular symptoms oc- 

 cur rather late in vitamin A deficiency, in the case of both animals and 

 man. '043 'lo^^ 



b'. Effect on the Respiratory Tract: Extensive keratinization occurs 

 early in the sequence of changes associated with avitaminosis A. This 

 involves the entire respiratory tract, from the nares to the bronchi. '"^^ 

 Bacterial invasion occurs, resulting in atrophy of the epitheUum and the loss 

 of cihary action, even before a replacement by keratinizing epithelium oc- 

 curs. According to Blackfan and Wolbach,^''''^ these conditions are re- 

 sponsible for lobar and bronchial pneumonia, which frequently is the im- 

 mediate cause of death, 'o^'* 



c'. Effect on the Gastrointestinal Tract: Although the esophagus may 

 become hyperkeratotic, changes in the epitheUa of the stomach and intes- 

 tine are shght, and the cells do not undergo keratinizing replacement. A 

 keratinizing metaplasia may be observed in the pancreatic ducts, but not 

 in the biUary ducts. ^"^^ 



d'. Effect on the Genitourinary Tract: In all species, a keratinizing 

 metaplasia occurs throughout the urinary tract, as well as in the epi- 

 didymis, uterus, oviduct, and sex glands. '"^^ The accumulation of keratin- 

 ized cells may result in obstruction of the urinary system. This may be 

 the immediate cause of death in rats suffering from vitamin A deficiency. 

 Grossly visible lesions of this type have been reported in human infants and 

 adults as welL^^^''^"** One of the first symptoms of deficiency of "the fat- 

 soluble vitamin," now known to be specifically a vitamin A deficiency, re- 



■0" K. D. Blackfan and S. B. Wolbach, /. Pediat., 3, 679-706 (1933). 



">" L. K. Sweet and H. J. K'ang, Am. J. Diseases Children, 50, 699-734 (1935). 



