129 



not sink to the bottom and thus have too thin a layer of 

 paraffin below them, put them in, with more melted paraffin, 

 and with a warmed dissecting needle arrange them in posi- 

 tion, i.e., not too near each other, and oriented with regard 

 to the sides of the paraffin block (that is to be). Cool the 

 paraffin quickly by floating the tray on cold water (use ice 

 water in summer), and, as soon as a sufficiently firm film has 

 formed over the top of the paraffin, by plunging the tray 

 into the water. In a minute or two the block will be hard 

 enough to permit of the unfolding and removal of the en- 

 veloping paper. Leave the paraffin block in the cold water 

 for ten or fifteen minutes at least, to harden thoroughly. 

 For very small specimens the imbedding can be done in a 

 watch glass. 



The specimens are now imbedded, and may be preserved 

 thus indefinitely. On a large piece of paper write a full 

 label, i.e., name of insect and character of specimen, locality 

 and date of capture, fixing agent employed, and other de- 

 tails of preparation that may be valuable to know, and wrap 

 up the paraffin block in this label. Such labelled and 

 wrapped up blocks can be conveniently kept in small 

 wooden or pasteboard boxes, labelled briefly outside with 

 name of the enclosed specimens. 



Instead of paraffin, collodion or celloidin is sometimes 

 used for infiltrating and imbedding. It is used especially, 

 however, for very large objects, i.e., objects more than one- 

 half inch in diameter. For small objects paraffin is better 

 because the sections can be cut thinner. For most insect 

 work paraffin is far the better medium. (For details of the 

 collodion method see Lee's Vade-Mecum, p. "120 et seq., and 

 Gage, p. 157 et seg.) 



Section-cutting. — The work of cutting sections with the 

 microtome can best be learned by the student by seeing such 

 work done. The differences in construction of microtomes 



