ORIGIN AND FATE OF OSTEOCLASTS 321 



alveoli where active bone resorption is preparing for the accom- 

 modation of the rapidly growing teeth. Here osteoclasts appear 

 in large numbers. 



The material which proved most useful consisted of several 

 series illustrative of tooth development in the pig. In these 

 decalcified preparations the histological preservation was excep- 

 tionally good. The jaws of appropriate pig embryos were fixed 

 in Zenker's fluid, decalcified in acid, embedded in celloidin, 

 and stained with hematoxylin and eosin or hematoxylin and 

 orange G. Hematoxylin and Congo red have been employed 

 also, but the hematoxylin-eosin combination was favored for 

 bringing out delicate tinctorial contrasts. Part of the material 

 comprised serial sections; in view of the large size of the osteo- 

 clasts, such series are instructive and important. 



Typical stages illustrative of the history of these elements 

 were demonstrated before the thirty-third session of the Ameri- 

 can Association of Anatomists at New York. 



OBSERVATIONS 



The osteoclasts (named 'Ostoclast' by Kolliker) are large, 

 multinucleate cells of irregular shape and without a definite 



I have maintained that, except in the youngest stages of bone development, the 

 reverse is true. Furthermore, those giant cells resulting from osteoblastic fu- 

 sion are traced by Jordan only from young, slightly differentiated cells; in my 

 membrane bone material these stages of osteoclast genesis have never been found, 

 for example, among the active osteoblasts of growing spicule tips, but only far- 

 ther back amid more or less 'depleted' cells; the term 'depleted' is, of course, rela- 

 tive, and need not necessarily signify 'worn out' — a term not of my using. In 

 the first preliminary announcement of these studies ('17 a) I recorded the abun- 

 dance of degenerative stages and intimated a probable final disappearance, but 

 further added the tentative observation that "indications of a transformation 

 into marrow reticulum are not lacking." At the time this last statement was 

 penned I had studied the fate of osteoclasts only partially, but had noted the re- 

 semblance of fragmenting osteoclasts like figure 18 to those stages held by Jackson 

 ('04) to depict a retransformation into marrow reticulum. In a later publication 

 ('18) and in the present report these stages are believed to represent merely de- 

 generating cells undergoing disintegration ('18, p. 237): "Neither have I seen 

 convincing stages of a fragmentation into reticular cells of the marrow as Jackson 

 and Maximow describe. The entire picture, from the early formation by the 

 fusion of depleted osteoblasts, seems rather to depict a progressive degeneration, 

 culminating in death and removal." 



