HYPOVITAMINOSIS A (aVITAMINOSIS a) 599 



placement or upon endochondral bone formation ceases during the de- 

 ficiency. ^"^^ 



Secondary symptoms may occur as a result of the abnormal bone growth. 

 In the petrous bone of the dog, a continuation of the appositional bone 

 growth causes a compression of the eighth nerve/"*^''"^^ resulting in deaf- 

 ness. ^°^^ However, this does not occur in the rat.'"^^ Moore^^^'' reported 

 blindness in calves as a result of compression of the optic nerve, but this, 

 also, has not been observed in rats.'''^^ In the case of the rabbit, certain 

 malformations occur in the bones of the ear following long-continued vita- 

 min A deficiency.'"*^ Accordhig to Mellanby,'"^- vitamin A deficiency 

 causes skeletal changes in dogs, due to its effect upon the position and ac- 

 tivity of osteoclasts and osteoblasts. When vitamin A therapy is re- 

 sumed, the sequences in bone growth return to normal, although the order 

 in which the resumption of normal activity takes place has not been dem- 

 onstrated. According to Wolbach and Bessey,'"" the epiphyseal se- 

 quences promptly return to normal in the vitamin A-deficient rat after 

 vitamin therapy is started. 



Vitamin A plays an important role in the case of all animals. It is neces- 

 sary for growth and differentiation of epiphyseal cartilage; it is likewise 

 required for differentiation of many epithelial structures, but is not con- 

 cerned with their growth. In addition to the above important functions, 

 vitamin A is primarily concerned with black and white vision, and also 

 with color vision. When deprivation of vitamin A occurs, all of these func- 

 tions operate with impaired efl&ciency, or they may entirely cease. 



(3) Deficiency Symptoms in Man 



a. Introduction. Two categories of vitamin A deficiency are recognized 

 in human nutrition, namely "primary" and "secondary. '""^^ The first 

 condition obtains when the deficiency results from an inadequate intake of 

 vitamin A or of carotene. The "secondary "avitaminosis A results when 

 there are: (1) disorders which interfere with the absorption of vitamin A 

 and carotene, as for example celiac disease, cystic fibrosis of the pancreas, 

 sprue, giardiasis, congenital absence or obstruction of the bile duct, cir- 

 rhosis of the fiver, severe diarrhea, and ulcerative colitis, (£) disorders 



loss E. Mellanby, /. Physiol., .94, 380-398 (1938). 

 1069 E. Mellanby, /. Physiol., 99, 467-486 (1941). 

 '»«« L. A. Moore, J. Nutrition, 17, 443-459 (1939). 

 ">«> H. B. Perlman, Arch. Otolaryngol., SO, 20-35 (1947). 



1062 g Mellanby, A Story of Nutritional Research: The Effect of Some Dietary Fac- 

 tors on Bones and the Nervous System, Williams & Wilkins, Baltimore, 1950. 



