244 



VITAMIN D GROUP 



calcified fasicles. These calcified matrix columns in due time become trans- 

 formed into true bone. In rickets, the V)lood vessels attack several fasicles 

 together, and invade the very thick partitions. In severe cases an entire 

 bush of capillaries, branching from large arteries and attacking widespread 

 areas of the cartilage matrix, may cause gross defects in some parts of the 

 cartilage plate, while in other, perhaps adjoining areas, there may be a 

 mass of cartilage cells. Only the heaviest partitions remain, and the osteo- 

 blasts settle upon these and cover them with osteoid. 



Wolbach^^ explained the occurrence of this abnormal calcification and 



Fig. 20. Advanced ricketh. Aluiked widening and irregularity of epiphyseal line 

 irregular vascular invasion, and defective calcification and ossification at chondro- 

 osseus junction. Osteoporotic appearance of metaphyseal region. 



these changes at the chondro-osseus junction as folloAvs: The capillaries 

 invade those regions which are uncalcified or soft, and after their penetra- 

 tion grow into large vessels, drawing aw^ay the circulation from the calcified 

 areas. Park believes, however, that the compressed cartilage cells we have 

 already described form the chief obstruction to the advancing capillaries. 

 The abnormal penetration of the blood vessels results in a variable blood 

 supply to the different parts of the cartilage, and the sections suffering from 

 insufficient blood may develop abnormally. Aside from the change of the 

 cartilage into osteoid rather than bone, there appear also bizarre, degenera- 

 tive forms of cartilage cells. The cells may vary greatly in size and shape, 

 with occasional appearance of double nuclei. At first these cells stain heavily 



" S. B. Wolbach, J. Am. Med. Assoc. 108, 7 (1937). 



