236 VITAMIN D GROUP 



sence of phosphatase or in tissue heated to a temperature which destroys 

 it. Moreover, the optimal pH for phosphatase activity is much beyond the 

 pH of normal tissue fluids. Third, calcification in vitro will fail to occur 

 when cells are poisoned, although such substances may not affect phos- 

 phatase activity. 



Endochondral calcification takes place in the presence of an adequate 

 concentration of plasma calcium and inorganic phosphorus. Deficiency of 

 inorganic phosphorus in rickets apparently cannot be made up by the local 

 action of alkaline phosphatase or phosphorylative glycogenolysis in the 

 hypertrophic cartilage cells under the same conditions. 



Since all tissue fluids presumably have the same concentration of calcium 

 and inorganic phosphorus, there still remains the question of why certain 

 tissues can be mineralized whereas this occurs in others only under abnormal 

 conditions or not at all. Rubin and Howard •'^ have demonstrated the pres- 

 ence of a mucopolysaccharide resembling chondroitin sulfate in tissues 

 potentially capable of undergoing calcification. This metachromic staining 

 material seems to form a combination with calcium and this may be the first 

 step in the process of calcium salt deposition. During the course of this 

 process the mucopolysaccharide seems to disappear and the tissue loses its 

 peculiar staining characteristics. This has been cited as a point against its 

 importance in primary calcification by Sobel,*^^ but Rubin and Howard^'' 

 have shown that the polysaccharide does not disappear during calcification 

 but can be stained and its presence thus proved, if the section is decalcified 

 before staining. 



Although much has been learned concerning the mechanism of mineral 

 salt deposition, little is known regarding the morphology, the chemical com- 

 position, including the enzyme content, and the metabolism of the organic 

 matter of bone, including the cartilage matrix and osteoid upon which the 

 calcium salts are deposited. Much has been added to our knowledge by the 

 use of special dyes and the ordinary light microscope, and this information 

 has been broadened and extended with the aid of the wide-angle diffraction 

 pattern and the electron microscope. The use of special dyes that react 

 specifically Avith certain constituents of the cell and the application of 

 enzymes that are specific cytoplasmic components afford further insight 

 into the functioning of osteoid and cartilage cells. Studies dealing with the 

 effects of vitamin C deprivation on osteoid structure and composition in 

 animals has thrown light on the mechanism of protein synthesis of cell 

 cytoplasm that may have far-reaching implications for cells in general. ^^ 



Cartilage matrix which under the ordinary light microscope and with the 



^^ P. S. Rubin and J. E. Howard, Trans. 2nd Conf. Metabolic Interrelations p. 155 



(1950). 

 68 R. H. Follis, Jr., Trans. 4th Conf. Metabolic Interrelations p. 11 (1952). 



