142 T. H. BAST 



The value of this type of preparations may be summed up 

 as follows: 



1. Bones need not be decalcified to obtain preparations fit 

 for oil immersion study. 



2. No sections need be cut but bone can be .studied in its 

 entirety. 



3. Bone can be examined fresh with water immersion lenses. 



4. The bone cell and its processes can be viewed with great 

 clearness without being subjected to the severe and distorting 

 action of acids. 



OBSERVATIONS ON BONE CELL STRUCTURE 



We shall not describe the osteoblast but the bone cell only. 

 However, it is often rather difficult to determine where the osteo- 

 blast stage ends and the bone cell stage begins. Lewis and 

 Stohr describe the beginning of the bone cell as follows; ''Osteo- 

 blasts .... form bone only along that surface which is 

 applied to the matrix. As the strand of bone grows broader 

 through their activity, it encloses here and there an osteoblast, 

 which thus becomes a bone cell." Since this seems to be the 

 generally accepted view we shall take as a criterion the point 

 where the rounded osteoblast is replaced by the star-shaped 

 body completely surrounded by an osseous matrix. 



The pieces of bone for this study varied in thickness from 

 one to four times the thickness of the bone cells. In such prep- 

 arations cells are found at various levels. With a 16 mm, 

 objective the cells appear very small, and since a low^ power lens 

 permits a considerable depth of focus several layers of cells are 

 brought into view often confusing the true relationship. The 

 4 mm. and the oil immersion lenses are used to better advantage, 

 the oil immersion giving the most satisfactory results. The 

 depth of focus is much less than the diameter of the cell 

 and so a clear focus can be obtained on any part of the cell. 

 The structures lying below or above a given focus appear quite 

 transparent when a strong light and an open diaphram are used. 

 Only those cells which lie in the same plane of focus are visible. 



