128 



poured. Place this dish on top of the paraffin* oven (a 

 water-bath oven heated at a constant temperature, a little 

 above the melting point of the paraffin used) and drop into 

 it several small pieces of paraffin. This paraffin will slowly 

 dissolve in the cedar-wood oil or xylol and this mixture will 

 penetrate the specimens. After the paraffin is all dissolved, 

 add more paraffin and remove the dish to the interior of the 

 oven. Leave here for from three to six hours, depending on 

 size, and density, of chitinous integument. Then remove 

 the specimens to a similar small dish of melted pure paraffin 

 and keep in the oven for from six to twenty-four hours. 

 The kind of paraffin to use depends largely upon the charac- 

 ter of the specimens. For very delicate specimens, a paraffin 

 of low melting point is desirable. But for most insect work 

 a hard paraffin is desirable, say paraffin of melting point of 

 about 55° Centigrade. In the summer, hard paraffin must be 

 used for the sake of ease in cutting. 



Another common method of infiltrating with paraffin is to 

 remove the specimens from pure xylol or cedar-wood oil to a 

 mixture (prepared beforehand) of one-half paraffin and one- 

 half xylol or cedar-wood oil. Leave in this mixture, in the 

 oven, for from three to six hours, and then remove to pure 

 melted paraffin and leave, in the oven, for from six to twenty- 

 four hours. 



After the objects are thoroughly infiltrated with pure 

 paraffin they must be imbedded. Make a small oblong 

 paper tray (see Lee's Vade-Meciim^ p. 91) and pour into it a 

 little melted pure paraffin ; when the paraffin has thickened 

 a little by cooling, so that the objects when put into it will 



* The student must get acquainted with the paraffin oven from an inspection 

 of that oven which happens to be in use in the laboratory. With much varia- 

 tion in size, shape, and elaborateness of make, all the different ovens in use 

 are essentially simply water-baths with an automatic thermostat for maintaining 

 a constant temperature. 



