127 



Hardening. After killing and fixing and washing the 

 specimens are kept in alcohol of 85$ strength. The speci- 

 mens may be kept thus indefinitely. Specimens which are 

 to be prepared for immediate cutting must now be hardened. 

 (If the specimens are to be stained /// toto, the staining should 

 now be done before removal to the 95$ alcohol. For direc- 

 tions, see p. 137.) Remove the specimens to 95$ alcohol 

 and leave for twenty-four to forty-eight hours, depending 

 upon size of specimen and degree of chitinization of integu- 

 ment. Then remove to absolute alcohol for from twenty- 

 four to forty-eight hours. The specimens, if properly fixed, 

 will now be thoroughly hardened. 



Clearing. (For theory and practice of clearing, see Lee's 

 Vade-Mccmn, p. 64 et seq.} Remove the specimens from ab- 

 solute alcohol to a vial which has been half-filled with xylol 

 and then filled with absolute alcohol. Put the specimens 

 into the vial and leave them for twelve to twenty-four hours. 

 Then remove to a vial filled with xylol and leave them 

 until cleared. This will require from twelve to twenty-four 

 hours. 



We have used cedar-wood oil a great deal for clearing, as 

 follows : Remove the specimens from absolute alcohol to a 

 mixture of absolute alcohol, one part, cedar-wood oil, one 

 part, for twenty-four hours. Then remove to pure cedar- 

 wood oil for twenty-four hours. 



Chloroform, which has been much used, is rather decried by 

 the present-day workers. For insects it should be avoided, 

 as it has little penetrating power. 



Infiltrating with paraffin, and imbedding. After 

 clearing, the specimens are to be infiltrated with melted 

 paraffin. The specimens should be removed from the vial 

 of cedar-wood oil or xylol into a small dish (watch-glass, 

 beaker, evaporating dish, casserole, tin "pattie" dish), into 

 which part of the cedar-wood oil or xylol from the vial is 



