6G2 X. VITAMINS D 



adult osteomalacia is due to lack of \dtamin D or to a contributory shortage 

 of calcium and phosphate in the diet, as is rickets. The chief pathologic 

 difference between the two conditions is that osteomalacia is manifested 

 by a decalcification of the bone, rather than by inadequate calcification of 

 the growing end of the bone as observed in the rachitic infant. Both condi- 

 tions respond to treatment with vitamin D. 



b. Vitamins D in Relation to Calcium and Phosphate Metabolism in 

 Species Other Than Man. The effect of rickets on the utilization of cal- 

 cium and phosphate in dogs and chickens appears to be the same as in 

 avitaminosis D in man. However, the metabolism of these inorganic 

 constituents in the rat appears to differ markedly from that in other species. 



Mellanby^* demonstrated in 1921 in his classical studies on puppies that 

 rickets is a deficiency disease in this species; it was reported that the fecal 

 calcium progressively approached the level of the ingested calcium during 

 the development of the disease. In a later study, Mellanby-^^ showed that 

 a reduction of the positive calcium balance occurred as a result of the 

 increased fecal excretion of calcium, concomitantly with the development 

 of the rickets. According to Wanscher^^^ and to McChesney and Giaco- 

 mino,^^^ the effect of \atamin D on the absorption of calcium and phosphate 

 is the same in the chick as it is in children and puppies. 



In contradistinction to the decreased absorption of calcium and phos- 

 phate during rickets in man, dogs, and chicks, the rat, at least during its 

 period of rapid growth, presents no comparable picture. It has been 

 demonstrated that, even during advanced rickets, rats can absorb con- 

 siderable quantities of calcium and phosphate. Under ordinary conditions 

 rickets could not be produced in this species merely by the omission of 

 vitamin D from the diet, but it was necessary that the Ca:P ratio be 

 unbalanced. Rickets would then occur in the absence of \dtamin D when 

 the Ca : P ratio was high or when it was low. However, the hypertrophic 

 uncalcified cartilage was found to be much more pronounced on diets hav- 

 ing a high Ca:P ratio; therefore this dietary procedure has usually been 

 employed in the study of experimental rickets. Dikshit and Patwardhan^^" 

 suggested that calcification depends mainly upon the state of the cartilage 

 cell and matrix. Vitamin D probably influences either the metabolism or 

 the structure of the epiphj'seal cartilage cell and osteoblasts, and their 

 matrices, rendering them capable of laying dowTi the bone salt. 



268 E. Mellanby, /. Physiol. 109, 488-533 (1949). 



2B9 o. Wanscher, Thesis, A. Busck, Nyt Nordisk Forlag, Copenhagen, 1939; cited by 

 R. Nicolaysen and N. Eeg-Larsen, Vitamins and Hormones, 11, 29-60 (1953), p. 33. 

 260 p. K. Dikshit and V. N. Patwardhan, Indian J. Med. Sci., 6, 107-116 (1952). 



