GENERAL METHODS. 35 



has near one end an object to be cut. The opposite end is 

 to be put into the object-carrier of the microtome. But 

 first the end containing the object is to be so trimmed 

 down that, while the object is still wholly enclosed in paraf- 

 fine, the surface to be cut shall be rectangular and as small 

 as possible. In cutting, this rectangle should be so placed 

 that two of its sides are parallel to the edge of the micro- 

 tome knife, which is placed at right angles to the direction 

 of its motion. 



49. It may be observed here that small blocks of paraffine 

 can be easily attached to rectangular blocks of cork, which 

 may then be fixed in the object-carrier of the microtome. 

 It is only necessary to place a few drops of melted paraffine 

 on one face of the cork and then to quickly put the paraffine 

 block upon it and, by running around its edges a heated 

 metal instrument, to cause it to be completely attached to 

 the block. This proceeding is especially convenient if one 

 wishes to change abruptly the direction of sections, as from 

 transverse to longitudinal. If it is desirable to cut off the 

 paraffine block for this purpose, it may be done with a knife 

 heated over a flame, as in this way the crumbling of the 

 paraffine is prevented. 



For preserving blocks of paraffine, the boxes used for the 

 so-called Swedish matches are convenient ; [or any small 

 pasteboard boxes.] 



ia. Imbedding in Celloidin. 



[4pa. While the above-described imbedding method and 

 medium are unquestionably of the first value in both animal 

 and vegetable histology, the use of celloidin as an imbedding 

 medium has recently become so extended, and the service 

 it renders in many cases where paraffine does not do well, 

 is so good that some account of the manner of its employ- 

 ment should be given here. It has the advantage that no 

 heat is required in the process of imbedding, and that very 

 large sections may be cut ; and the disadvantage that the 

 knife must be kept wet while cutting, and that the thinnest 



