BONE CELLS AND BONE RESORPTION 473 



100 units of the extract was administered in 3 or 4 doses over a 

 period of 7 to 8 hours in suckUng rats between 5 days and 2 weeks 

 of age at the time of injection. When weanHng rats were used (3 

 to 4 weeks of age), the dose was increased to a maximum total of 

 200 units administered over an 8-hour period. The costo-chondral 

 junction of ribs, the tibiae (both regions sectioned longitudinally), 

 and the parietal bones of the cranial vault (sectioned coronally) 

 have been examined. Unless specifically stated otherwise, specimens 

 were fixed in Bouin-Hollande solution for 3 days, decalcified in 18.5 

 per cent versene at pH 7, double-embedded in celloidin-paraffin, 

 sectioned at 5 microns, and mounted in Permount. 



The following analyses were carried out on this material. 



Histological Stains 



Sections were stained with hematoxylin and eosin, chrome hema- 

 toxylin-phloxine, Masson's trichrome, Bodian's silver (Gridley, 

 1960), Gomori's silver (Romeis, 1948; fixation 10 per cent formalin 

 in 95 per cent ethanol for 24 hours), and toluidine blue (fixation 

 in Rossmann's fluid at 4°C overnight; 0.1 per cent aqueous stain, 20 

 minutes at 45°C, with and without alcoholic differentiation). 



Methyl Green-Pyronin 



Bones were fixed in 10 per cent neutral formalin for 16 hours, and 

 stained with methyl green-pyronin Y, according to Brachet ( Pearse, 

 1960). Some sections were incubated in a ribonuclease (Worthing- 

 ton Biochemical Corporation ) solution ( 1 mg/ml distilled water ) 

 at 37°C for 3 to 4 hours, or in water alone under the same condi- 

 tions, prior to staining. 



Periodic Acid-Schiff 



Bones were fixed in Rossmann's fluid at 4°C overnight, and de- 

 calcified in 2 per cent nitric acid in 80 per cent ethanol. Sections 

 were spread on 70 per cent ethanol, dried at 37°C, coated with 1 

 per cent celloidin, and stained with periodic acid-Schiff (PAS). 

 Some sections were incubated in saliva or in water at 37 °C for 1.5 

 hours, prior to staining. All sections were counterstained with hema- 

 toxylin, and mounted in Canada balsam. 



