\ii. \ii'\Mi\ A i)i;fi<ii:\(v i\ animals 111 



arable. Vhc sv{\\iv\\vvs dv>cv\\)vd l)y .lohnsoii coincide so well with the 

 liiadual increase of intraeranial pressuie icsnltinj^ tVoni ictardatioii of 

 jirowtli of the skull and unretarded growth of tlie nerxous system that a 

 mechanical exphmation seems unavoidable. ' 



The epithelia of cornea and bulbar and i)alpebral conjunct i\-ae V)ecome 

 keratinized. Blood ves.sels grow into tiic tunica propria of the cornea from 

 the liml)ic plexus concurrently with the epithelial changes, and are found 

 throughout the thickness of the cornea. Keratinizing metaplasia of the 

 ducts and atro[)hy of the lacrimal glands, together with the conjunctival 

 changes, result in loss of all secretions — .xerosis. Accumulations of kerati- 

 nized cells in the conjunctival sac e.xcite inflammatory reactions — xeroph- 

 thalmia. Edema and necrosis of the cornea — keratomalacia — may occur 

 beneath an intact hyperkeratotic epithelium. Bacterial infection favored 

 by the accumulation of keratinized cells results in ulceration of the cornea 

 and conseciuently hypopyon. On the whole, the gross ocular manifestations 

 in animals and in man appear late in the deficiency.^- ^'^ 



b. Respiratory Tract 



Keratinizing metaplasia of the entire respiratory tfact, nares to bronchi- 

 oles, occurs early. Cough is an early symptom in infants. Atrophy of the 

 epithelium and loss of ciliary action e\en l>efore rejilacement by keratiniz- 

 ing epithelium favor bacterial invasion, and hence lobular pneumonia has 

 been a frequent immediate cause of death. ** In deficient rats foreign par- 

 ticles — starch granules from the food, for example — are fretiuently foiuid 

 in the alveoli of lungs. The development of bronchiectases, atelectasis, and 

 keratinizing walled c.ysts are results inherent in the specific epithelia re- 

 sponse of the deficiency, as are involvement of the Eustachian tubes, 

 mifldle ears, and accessor}' respiratory siiuises. 



c. Alimentary Tract 



The epithelia of the mucosa of stomach and small and large intestines 

 do not undergo keratinizing replacement ; at most, slight degrees of atrophy 

 of gastric and intestinal glands can be found. The esophagus becomes hy- 

 perkeratotic. Keratinizing metaplasia (jf pancreatic ducts occurs but not 

 of biliary ducts (.see Fig. 28). The enamel organ of forming teeth in the hu- 

 man, and throughout life of the incisor teeth of rats and guinea pigs and 

 pre.sumably of all rodents, undergoes atrophy and keratinizing metaplasia; 

 the con-sefjuences will be described in succeeding pages. 



^ S. B. Wolhach and O. A. Bessey. Arcli. I'athul. 32, 689 (1941). 

 " K. D. Bhickfan and S. B. Wolbach, ,/. Pedial. 3, 679 (1933). 

 •0 L. K. Swoot and 11. .1. K'ang, Am. ./. Diseascft Childni, 50, 699 (1935). 



