148 VITAMINS A AND CAROTENES 



11 cases by Blackfan and Wolbach^^ (including the case described by Wilson 

 and DuBois), and 17 cases by Sweet and K'ang.^" 



1. PosT-MoRTEM Material 



These 29 post-mortems form the basis of our knowledge regarding the 

 internal pathology of vitamin A deficiency in man. These studies suffer 

 from the fact that in most cases vitamin A therapy had been instituted for 

 variable periods (less than 1 week in about one-third, and between 1 and 5 

 weeks in more than one-half of the cases) so that varying amounts of epi- 

 thelial repair had often occurred before exitus. However, 6 of the cases 

 studied by Blackfan and Wolbach^- were untreated cases of keratomalacia. 

 The findings in the separate pathologic studies are fundamentally the same, 

 and in general accord with those obtained in experimental studies. 



Considering the 29 cases as a group, it is of interest that approximately 

 two-thirds exhibited either xerophthalmia or keratomalacia, were less than 

 18 months of age, and succumbed as a result of bronchopneumonia. Three 

 young adults (18, 23, and 32 years of age), on vitamin A therapy for 2 to 5 

 weeks,^" were the only subjects over 4 years of age. On the whole, the extent 

 of epithelial alteration was quite commensurate with the severity of defi- 

 ciency manifestations and the extent of vitamin A therapy. Conclusions 

 and deductions which may be made from the pathologic studies reported 

 are as follows. 



2. Epithelial Metaplasia 



In general, keratinizing metaplasia of epithelia of internal surfaces of the 

 body is a relatively late manifestation of avitaminosis A. Whether the 

 susceptibility of these epithelia varies in relation to age has not been 

 established. The metaplastic change may in some instances be quite wide- 

 spread and in other cases restricted to localized patch-like areas. 



The "respiratory epithelium," lining most of the respiratory system, 

 seems especially prone to keratinizing metaplasia; it is also slower than 

 other epithelia in effecting full morphologic restoration after vitamin A 

 therapy. This is compatible with the highly specialized character of this 

 pseudostratified columnar epithelium, with an abundance of ciliated and 

 mucous cells and a surface bathed by secretions from many underlying 

 mucous and mucoserous glands. The metaplasia of this epithelium consti- 

 tutes the most impressive evidence of the role of vitamin A in maintaining 

 the functional and structural integrity of specialized epithelia, and the 

 particular susceptibility of mucus-secreting cells to lack of vitamin A. 

 Keratinization and blockage of ducts may lead to dilation and hypofunction 

 of the underlying glands. The adjacent mucosa is often the site of infiltra- 



82 K. D. Blackfan and S. B. Wolbach, J. Pediat. 3, 679 (1933). 



