ORIGIN AND FATE OF OSTEOCLASTS 329 



the time of resorption of the milk teeth an osteoblastic history- 

 is likewise excluded. In the present communication are re- 

 corded observations of osteoclasts in continuity with the marrow 

 reticulum; it is entirely probable that this is not a secondary 

 union, but primary, and of developmental significance. My 

 chief results, nevertheless, point to a widespread formation of 

 osteoclasts in the later stages of development from osteoblasts 

 and bone cells. 



Polykaryocytes which resemble osteoclasts morphologically 

 are the so-called foreign-body giant-cells produced within the 

 body about fat (Mallory, '11) as a center, or developed experi- 

 mentally about introduced foreign bodies, such as agar, paraffin, 

 lycopodium spores, or bone dust (Maximow, '02; Lambert, '12; 

 Mallory, '11, et al). These are said to form from fused, wan- 

 dering leucocytes, and Mallory ('11) even goes so far as to derive 

 all osteoclasts (but on insufficient evidence) from a like source. 

 The foreign body origin is, nevertheless, an important concept. 

 It seems reasonable that on the cessation of active growth a 

 spicule of bone, or any quiescent portion of a spicule, becomes 

 essentially a foreign body and the cells in contact with it, not 

 necessarily all of one origin, may respond to whatever stimulus 

 it offers and fuse into syncytial masses. Kolliker (73) found 

 that ivory pegs driven into bone became eroded, the lacunae 

 thus formed containing polykaryocytes. Rustizky (74) sim- 

 ilarly produced giant-cells, but no lacunae, by introducing pieces 

 of bone in the dorsal lymph sacs of frogs. 



The causative factors of giant-cell formation are necessarily 

 obscure. Kolliker considered it due to a pressure by the soft 

 parts underlying bone (compare also Wegner). Pommer ('81), 

 on the contrary, held as responsible a locally increased blood 

 pressure. On spongy bone, at least, it may be due to the aug- 

 mented mutual pressure resulting from the decreased size of the 

 spicules and to a concomitant loss of cell individuality as a result 

 of general osteoblastic degeneracy. The formation of ordinary 

 foreign-body giant-cells would demand a different explanation. 

 Presumably a definite thigmotaxis is operative in all giant-cell 

 formation. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 20, NO. 3 



