210 THE AMERICAN MONTHLY [July 



applying a little balsam to the edge of the cover, and ac- 

 curately centre it on the turntable. Place and arrange 

 the objects on a thin coating of balsam in the centre of 

 the cover. When dry and set, the objects may be com- 

 pletely covered with balsam and put into the dry oven 

 until hardened. If the objects are white a layer of Bruns- 

 wick black is now laid all over the balsam ; if the objects 

 are black white zinc cement should be used. In either 

 case care should be taken to lay them on in thin coats, 

 and allow to dry in the open air before the next layer is 

 applied. Now remove the glass-cover from the slip by 

 slightly heating it. It may now be turned over and mount- 

 ed on the cell designed for it. Gelatine dissolved in 

 water, with enough alcohol added to liquefy it from the 

 jelly state, is a good preparation for fastening the cover 

 to the cell. — Knowledge. 



The Celloidin Process of Section-Cutting. 



H. WALKER. 

 There is some diversity of opinion as to the relative 

 merits of celloidin and paraffin for imbedding purposes. 

 The latter is, undoubtedly, the most universally used, 

 and, in the hands of an expert manipulator, produces very 

 brilliant results. I have usually found that, when one 

 begins with paraffin, it is rarely discarded for any other 

 substitute, and the same applies pretty much to the use 

 of celloidin. Still, there are exceptions, and the student 

 must be guided pretty much by individual experience. 

 Thus, I have found that when there is a chitinous integu- 

 ment of more than average hardness, as in some bees, it 

 is very apt to break away from the surrounding celloidin, 

 and the entire section will often drop out. It has not suf- 

 ficient hold upon the polished surface, and, under the im- 

 pact of the knife, pulls away. For such preparations, I 

 recommend paraffin. Again, though very penetrative in 



