MAKING SECTIONS OF BONE AND TEETH. 329 



for some little time before they are mounted ; this dissolves 

 the grease, and makes the bone cells and their canaliculi much 

 more distinct. 



Fragments or chippings of fossil bones may be put into 

 balsam without any grinding; and as it generally happens 

 that in such bones aU the cells and canals are full of earthy 

 substance, it does not matter if the balsam have been made to 

 boil ; it is, perhaps, the better plan that this should be done, 

 as it makes the intercellular tissue more transparent, and the 

 bone cells, therefore, can be seen more distinctly. 



It may be as well here to state, that the sections shotdd, if 

 possible, be made in two or more directions; thus, for instance, 

 if the specimen about to be examined be a portion of the 

 shaft of a long bone, we should cut the first transversely and 

 the other two longitudinally ; one of the latter may extend 

 through the medullary cavity, and the other merely through 

 the outer or periosteal surface. The scales and thin plates of 

 bone of fishes wiU rarely require more than grinding down on 

 the hone ; if the surface of the scale be enamelled, as in the 

 Lepidosteus, the inner surface only may be rubbed down on 

 the hone, and the outer left with its natural polish of enamel 

 on it, the ground surface may be cemented to a slide by 

 Canada balsam, and the enamelled wiU then require no 

 covering either of thin glass or of balsam, but be kept in the 

 same manner as the fossil woods before described. In order 

 to obtain a perfect notion of the structure of bone, one or 

 more sections should be soaked in dilute muriatic acid to get 

 rid of the earthy matter, and others in caustic potash to destroy 

 the animal matter ; these should be mounted in fluid, and will 

 be found very instructive. 



To make Sections of Teeth. — The teeth of fishes not being 

 supplied with a layer of dense enamel, may be cut in the same 

 way as ordinary bone, with a fine saw, and then be rubbed 

 down between the hones, and polished in the usual manner ; 

 but those of nearly all the higher mammaha being coated more 

 or less with enamel of flinty hardness, will require a much 

 greater amount of labour to be expended on them. 



The saw best adapted for cutting through the enamel is 



