BONE CELLS AND BONE RESORPTION 483 



of osteoclasts observed on the surface of crania stained supravitally 

 with neutral red (cf. Young, 1959). At about 10 days of age and 

 thereafter, resorption becomes prominent within the vascular spaces 

 of the parietal bones in association with the development of the 

 diploe. 



Fig. 18. Rib shaft of a 10-clay-old rat, stained according to Bodian's silver 

 technique. Osteogenic surfaces (above) are characterized by a granular stain- 

 ing of the matrix. Osteocyte canaliculi are not stained within this new matrix, 

 but are clearly visible in the underlying, older matrix. Resorptive surfaces 

 (below) are sharply outlined, and are further distinguished by the staining 

 of associated canaliculi. ( X 800.) 



Fig. 19. Soft x-ray microradiogram of the tibial metaphysis of an 11-day- 

 old rat, injected with 100 units of parathyroid extract 1 day prior to sacrifice. 

 Growth cartilage is on the right, marrow cavity on the left. Note the apparent 

 fracture of the shaft (upper left). An increase in resorption in the zone of 

 trabecular resorption (left) has resulted in a shortening of the metaphyseal 

 trabeculae, and a similarK' accelerated resorption in the zone of cartilage in- 

 vasion (x) has led to the apparent disengagement of some trabeculae from 

 their normal attachment to the calcified parts of the growth cartilage. (X 80.) 



Fig. 20. Soft x-ray microradiogram of a part of the parietal bone of a 15- 

 day-old rat, injected with 100 units of PTE 1 day prior to sacrifice. Endocranial 

 resorption predominates in this region, in which development of the diploe has 

 not yet been initiated. A thin remnant of woven bone (arrow) is slightly 

 more heavily mineralized than the surrounding lamellar bone. Sites of prefer- 

 ential resorption (indicated bv the irregular surface, lower left) are unrelated 

 to these differences in calcification. The vertical line (center) results from a 

 crack in the section. ( X 200.) 



Fig. 21. Phase contrast photomicrograph of the left part of the section 

 from which the preceding microradiogram was made. Note the absence of 

 osteoid, and the presence of an osteoclast (arrow) apparently engaged in 

 resorbing bone of varying degrees of mineralization, (x 320.) 



Fig. 22. Parietal bone from an 18-day-old rat, injected with 150 units of 

 PTE 1 day prior to sacrifice. The animal had been given a single injection of 

 glvcine-H-^ at 6 days of age. A thin layer of woven bone, stained heavily 

 with periodic acid-Schiff, is present centrally. The matrix of the woven bone 

 is not labeled, indicating that it had been formed prior to the injection of 

 glycine-H^. Within this region, however, the walls of osteocyte lacunae are 

 reactive. Reaction bands (arrows) are present at the junction of the woven 

 bone and the thick layers of lamellar bone above and below. These heavily 

 labeled lamellae were formed within the first 4 hours after injection of gly- 

 cine-H'^. The remainder of the lamellar bone (which is weakly and diffusely 

 labeled) was formed subsequent to the injection. Accelerated resorption 

 within the diploe is unrelated to the age or histologic organization of the 

 matrix. Note that the ectocranial, but not the endocranial, surface (below) 

 shows an increased affinitv for the PAS stain. Autoradiogram, PAS-hematoxylin. 

 (X320.) ' _^^i^- 



A' 



&■ 



