51^2 N. M. IIANCOX AND B. BOOTIIROYD 



in electron micrographs. Obviously, the next step is to locate the 

 reaction product in the electron microscope. A further point of 

 interest is that the various osteoclasts present in a given culture 

 differ in their content of a particular enzyme. Some are strongly 

 positive, some weakly so, and others more or less negative. This 

 perhaps might be another example of the existence of different 

 degrees of "readiness" for phagocytosis as postulated by Holt and 

 Hicks (1961). 



Summary 



Electron microscopy seems to indicate that bone salt crystals are 

 somehow loosened from embryonic avian bone matrix and are swept 

 up into channels and vacuoles in the osteoclast; the exposed collagen 

 is enclosed in folds of the ruffled border in a way which strongly 

 suggests a process of continuous digestion. Cytochemical work with 

 the light microscope shows that lysosome-like hydrolytic enzymes 

 occur in the cells. But much more information is needed, particu- 

 larly about the shift of crystals and about the enzyme cytochemistry 

 of the cell at the electron microscope level. 



References 



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Burstone, M. S. 1960L>. Histochemical demonstration of succinic dehydro- 

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