116 VITAMINS A AND CAROTENES 



sequences serve to identify inclusions of odontogenic epithelium in the pulp 

 by restored morphology of the cells and calcareous deposits. They also 

 explain, as the result of bending and folding of the odontogenic epithelium 

 at or near the formative end, through resumption of normal processes, the 

 tooth duplications and tumor-like formations reported by Burn et al}- 



Changes in a tooth "germ" of a human infant who succumbed to vitamin 

 A deficiency, comparable in nature to those of rodent incisor teeth, have 

 been described.-^ 



Thus far, no relation between endocrine physiology and the specific 

 morphologic manifestations of vitamin A deficiency has been established. 

 Ovaries and testes have been mentioned above. 



i. Endocrine Organs 



The adrenals, the islands of Langerhans, and the thyroid and parathyroid 

 glands undergo no noteworthy morphologic change. In spite of the severe 

 inanition of long-continued vitamin A deficiency, the adrenals remain small 

 and show, in both rats and guinea pigs, some evidences of atrophy in con- 

 trast to the enlargement resulting from simple underfeeding, particularly 

 in guinea pigs.-^- ^^ 



The adrenal and thyroid glands will be considered briefly in the section 

 on hypervitaminosis A. 



2. Bone, Postnatal 



After grow^th of the skeleton is completed, vitamin A deficiency has no 

 specific effect upon bone structure. In grooving animals — rats, guinea pigs, 

 mice, dogs, and fowl — there are prompt and specific effects which result 

 in retardation of skeletal growth and interference with growth patterns of 

 bone which are distinguishable from the conseciuences of inanition, whether 

 produced by inadequate amounts of a complete diet or by other vitamin 

 deficiencies. Deficiency of vitamin A is the only known means of causing 

 severe retardation of skeletal growth before causing appreciable retardation 

 of growth of soft tissues, including the nervous system.^' *" 



Skeletal growth changes in the human infant due to vitamin A deficiency 

 have not been studied. The following account is based upon extended 

 studies on albino rats and has been confirmed for the guinea pig, the dog, 

 the duck, and the chick. Epiphyseal cartilage sequences are promptly re- 

 tarded and cease entirely in long-continued A deficiency. All growth of the 

 skeleton dependent upon replacement or endochoiulral bone formation 



22 C. G. Burn, A. U. Orton, and A. H. Smith, Ydlr ./. Hi,il. and Mvd. 13, 817 (1941). 



23 P. E. Boyle, ./. Dental Research 13, 39 (19;«). 



2" H. T. Blunienthal and L. Loeh, Am. J. Palhol. 18, (315 (1942). 

 25 R. Whitehead, J. Palhol. and Bacterial. 54, 1(19 (1942). 



