316 LESLIE B. AREY 



analysis of the evidence upon which their alleged bone-resorp- 

 tive potentiality rests. 2 



The literature concerning polykaryocytes is voluminous, 

 many accounts dealing confusedly with those of normal and 

 pathological occurrence. Observations and speculations on the 

 giant-cells of normal bone development, of bone tumors, and on 

 those of other pathological origins so overlap that a complete 

 literature review would be both tedious and unprofitable. For 

 this reason the following digest of previous work will deal chiefly 

 with the osteoclast associated with normal bone development 

 and resorption. 



HISTORICAL 



Origin. Views as to the origin of the osteoclast are not in 

 accord. 



Kolliker ('73) observed the presence of osteoclasts on resorp- 

 tion surfaces; these appeared at first discontinuously in the 

 osteoblastic layer and increased in number, size, and multinu- 

 clearity concomitantly with the disappearance of the latter. 

 Admitting the absence of direct proof by observation, he never- 

 theless considered the circumstantial evidence sufficient to render 

 the genetic relation of osteoblasts to osteoclasts highly probable. 

 The latter were supposed to represent single osteoblasts which 

 had undergone repeated nuclear division. For the earliest 

 osteoclasts, and for those found during the resorption of milk 

 teeth, an origin from connective-tissue cells was assumed. 



2 Shortly before his death Prof. C. W. Prentiss had been engaged upon a 

 study of the osteoclasts. Except for a brief abstract ('15) of a paper on this 

 topic delivered before a local surgical society and for a number of unlabeled draw- 

 ings, there were found no notes or other data to indicate the extent or state of 

 completion of the project. For these reasons the perhaps tentative conclusions 

 reached by him are known in outline only. On assuming duties at this labora- 

 tory the writer became interested in the same problem and worked over the 

 entire field independently; some of the preparations used have been identified as 

 those upon which Professor Prentiss made observations. It is believed that the 

 scope of the investigation has been extended considerably and that certain in- 

 terpretations have been profoundly modified. With respect to an osteoblastic 

 origin our conclusions are in accord, but as to the fate and significance of the ele- 

 ments our opinions clearly differ. 



