EFFECTS ON THE VISUAL APPARATUS 2IO, 



and (2) the formation of keratohyalin granules in the second layer of the epi- 

 thelial cells in the conjunctiva, but not in the cornea, except at the limbus. 

 These granules have also been described in xerosis conjunctivae in human 

 lagophthalmos. Later stages in the rats, as in human keratitis, show alterations 

 in the corneal epithelium, producing either an abnormal keratosis (due to the 

 drying), or a necrosis (from interference with nutrition). The epithelial cells 

 lose their nuclei and fuse, usually with infiltration by pus cells, and may disap- 

 pear in small areas. The substantia propria shows marked edema and diffuse 

 cell infiltration, which is denser in exposed areas. Cellular exudates also appear 

 in the anterior chamber and iris, and perforating ulcers often develop. Mori 

 ('23) claims that xerophthalmia and keratomalacia may be produced in rats 

 also by diets containing abundant vitamin A, but with certain unfavorable salt 

 mixtures. 



Yudkin and Lambert ('22) found the experimental xerophthalmia of young 

 rats presenting "watery lacrimation with a serosanguinous conjunctival secre- 

 tion, becoming after a short time somewhat viscid." Early focal lesions were 

 found always beginning in the conjunctiva, and consisting of degeneration 

 and cellular infiltration of the epidermis, sometimes extending into the sub- 

 jacent' stroma. The cornea is involved later. They also find ('22a) in the 

 lacrimal glands definite lesions, which appear degenerative or inflammatory 

 in character. The lesions include variations in the size, form and staining 

 properties of the lacrimal gland cells, which are probably correlated with 

 functional derangement. The disturbance of lacrimal secretion may account 

 for some of the phenomena of the xerophthalmia, particularly the characteristic 

 drying of the cornea in the later stages. 



More recent histological study by Lambert and Yudkin ('23) indicates that 

 the changes in the lacrimal and Meibomian glands of the rat during experimental 

 xerophthalmia are of doubtful significance. More definite degenerative and 

 inflammatory lesions occur in the Harderian gland. Disturbances in the 

 (probably fatty) secretion of this gland may render the conjunctiva more 

 susceptible to infection. 



Finally, Yudkin and Lambert ('23), from experiments on young white rats, 

 concluded that: 



"The earliest lesions in ophthalmia of rats resulting from deficiency of 

 vitamin A consist in focal inflammatory lesions in the conjunctivae of the lids 

 and nictitating membrane. The involvement of the cornea, which constitutes 

 the most conspicuous feature of the well developed ophthalmia, is a secondary 

 phenomenon. The characteristic corneal plaque consists of keratinized epithe- 

 lium beneath which the deeper layers of epithelium are generally found intact." 



"Pathologically the ocular manifestations of a deficiency of vitamin A 

 are referable to a low grade inflammatory process, originating in the palpebral 

 conjunctiva and spreading to the cornea. The rapidity of development and 

 the degree of destruction probably depend in large part on the type of bacterial 

 infection." 



Certain recent observations on the effects of dietary deficiency in vitamin 

 A upon the human eye remain to be considered. As previously stated, numer- 



