ORIGIN AND FATE OF OSTEOCLASTS 323 



Whereas the osteoclasts may arise in the early stages of bone 

 development from the mesenchymal or reticular cells of the 

 marrow, as Jackson ('04), Danchakoff ('09), and Maximow ('10) 

 contend, my observations indicate that in later stages they take 

 origin chiefly from the osteoblastic syncytia just described. 

 There were found all transitional tinctorial stages between 

 these syncytia with basophilic cytoplasm, staining blue with 

 hematoxylin, and typical oxyphilic osteoclasts, staining red 

 with eosin. In figure 2, compare the intermediate purple shade 

 of a very large-sized intermediate with the normal basophilic 

 osteoblasts at the right and with a typical osteoclast such as 

 figure 4. Here again this characteristic coloration does not 

 result from basic overstaining as may be convincingly proved by 

 an inspection of adjacent fields. 



A comparison of the nuclei found in osteoclasts and osteoblasts 

 can not be depended upon to furnish very reliable information 

 as to genetic relationship. Not only do the osteoclastic nuclei 

 commonly exhibit pyknosis, but the resemblance between the 

 unchanged vesicular nuclei and those of osteoblasts and con- 

 nective tissue is close; this is not surprising since the osteoblasts 

 themselves originate from the connective tissue. In some 

 instances, nevertheless, the chromatin disposition and general 

 nuclear structure of the osteoblasts and osteoclasts clearly 

 agree better than do either with the adjacent marrow reticulum. 

 There is evidence that the elongate nuclei in flattened osteo- 

 blasts are restored to the spheroidal configuration upon the 

 release of compression. 



Not only are basophilic syncytia and syncytial masses of 

 intermediate stainability found, but osteoclasts may be seen 

 frequently continuous at one or both ends with basophilic 

 osteoblasts and particularly with osteoblastic syncytia. This 

 is represented in figure 3, especially at the right; both osteoclast 

 and osteoblasts have been displaced artificially from the bone 

 surface. Figure 4 shows on the right an osteoclast with five 

 nuclei continuous by a bold transition with fused basophilic 

 osteoblasts. Similarly in figure 11, from a human fetus, the 

 osteoclast lapped over the end of a bone spicule, is abruptly 



