670 X. VITAMINS D 



inhibiting action in the intestine. For a further discussion of phytase, 

 the reader is referred to The Lipids, Vol. II, pp. 67 to 69. 



(4) The Action on Bone Formation 



There can be no doubt that \'itamin D exerts a profound effect upon 

 calcification of bone, and that it is able to correct the abnormal condition 

 of these structures in rickets. The question which many physiologists 

 have raised, and which is still unsolved, is whether or not the effect of 

 vitamin D on calcification is direct or whether it results indirectly from the 

 effect of the vitamin upon calcium metabolism.-*^ 



Vitamin D causes an increased deposition of bone salts in rachitic ani- 

 mals which can be demonstrated histologically or by chemical analysis of 

 the ash content of the bones. According to Wolbach and Bessey,^^^ 

 it is generally accepted that, in rickets (1) a failure of calcification of 

 cartilage columns in the so-called zone of provisional calcification, and 

 failure of calcification of the osteoid occur; (S) that a continued growth 

 and consequent increase in thickness of the diaphyseal cartilage and 

 osteoid result; (S) that there is a lack of vascular growth into the carti- 

 lage; (4) and that a resorption of bone formed before the deficiency in 

 this area takes place. Wolbach and Bcssey^^^ also state the undisputed fact 

 that experimental rickets in animals duplicates completely the spontaneous 

 disease in man and animals. 



However, one concept proposed by Wolbach and Bessey^^' is challenged 

 by Nicolaysen and Eeg-Larsen.^ This is the statement of the former 

 authors^^^ that rickets is due to the impaired absorption of calcium and 

 phosphate, and "that there is no reason to believe that the cells and matrices 

 concerned in bone growth and maintenance are defective in rickets or are 

 directly acted upon by the vitamin D." This generalized conclusion is 

 largely based upon the experiments of Shohl and Wolbach, ^^* and is 

 correct on the basis of the experimental results obtained. However, in 

 an extended study by Nicolaysen and Jansen,^i* data are presented which 

 lead to the conclusion that vitamin D does influence the structure, viz., 

 the matrices of the bones. The anatomical picture was strikingly different 

 in the presence and absence of vitamin D. Thus, a dense network of 

 trabeculae was always evident in the bones of the \ntamin D-deficient rats, 

 in contrast to the few trabeculae which were present in the case of vitamin 



313 S. B. Wolbach and O. A. Bessev, Physiol. Revs., 22, 233-289 (1942). 



314 A. T. Shohl and S. B. Wolbach, /. Nutrition, 11, 275-291 (1936). 

 3i« R. Nicola^'sen and J. Jansen, Acta Paediat., 23, 405-433 (1939). 



