Objects for the Microscope. 203 



is a small web saw, a good hone, and patience. Slice a 

 thin bit of bone with the saw, and rub it on the hone with 

 water until transparent. Towards the end of the operation 

 fasten the section with balsam to a glass slide, and finish 

 the grinding carefully, when it may be dried and mounted 

 like any other object. 



The whole jaw of a Mole well ground down is very beau- 

 tiful, showing the Haversian tubes like a tree branching 

 out between the fangs of the molar teeth. 



Longitudinal sections generally show the structure best. 



In the position and use of a bone, the size and number 

 of the lacuna and Haversian canals are modified to give 

 the required strength or lightness. The wing-bones of 

 Birds abound in Haversian canals and lacuna, which give 

 both elasticity and strength, and there is an interesting 

 paper on this subject by the Rev. J. B. Dennis, in the 

 ' Microscopical Journal ' for 1843. For the guidance of 

 the student who may wish to collect specimens and prepare 

 sections of bone, the following table of the relative size of 

 bone-cells in Fishes, Reptiles, Birds, and Man, will be 

 useful : 



Measurement of bone-cells in parts of an English inch. 



(TRANSVERSE SECTIONS.) 

 /T ,. f one of the largest ^ 



Human bone J^ gdiameter > 'Et 



Long diameter one J e lar Sf \ 

 one of tiM smallest 



Ostrich . . . . < -aou 



Short diameter ( one ^ e lar gf t > 

 tone of the smallest 4. 



Turtle ( Long diameter J one of the largest 



\ one of the smallest _i 



Reptile . .. . | Short diameter (one of the largest ^ 



(.one of the smallest i 



f Long diameter | one J fjj e Iar ^ st X 

 Conger Eel . . J \ one of the smallest ^ 



[Short diameter ( one ^^ e lar g est 



[one of the smallest T 



so e 



