CH. VII] 



PARAFFIN SECTIONING 



185 



It is hastened by warmth. It is then removed from the cedar-wood oil, drained, 

 and placed in pure, melted paraffin, and this is then put into a paraffin oven and 

 left from 2 to 24 hours (see Ch. X). It is then imbedded for sectioning.* 



Paraffin for infiltrating has usually a somewhat lower melting point than that 

 for imbedding. Equal parts of paraffin of 43 C. and 54 C, answer well. For 

 imbedding, the paraffin must be of a melting point which will give good ribbons 

 in the temperature of the room where the sectioning is to be done. In a room of 

 19 to 20 C. a mixture of 1 part 43 C. paraffin with two parts of 54 C. usually 

 answers well. 



Fig. 155. Hot filter for 

 paraffin, gelatin, balsam, etc. 

 It is entirely surrounded by a 

 water jacket. The water is 

 heated by placing a burner imder 

 the projecting part H. The 

 wire basket is to hold the strainer 

 and allow a free flow of the 

 filtered substance on all sides. 

 There is a bail for suspending 

 the filter, and the filtered sub- 

 stance rims out through the 

 narrowed part F. 



\ 287. Imbedding in Paraffin. — Make a small paper box, fill it nearly full 

 of hot paraffin, place the box for a half minute on some cold water to make a 

 thin solid layer on the bottom, then transfer the tissue to the box and arrange 

 near one end so that the sections may be cut in the desired plane. Now pi ace the 

 paper box on as cold water as possible so that the paraffin may cool quickly. It 

 will be more homogeneous if cooled quickly, and will shrink tightly against the 

 tissue and avoid air spaces. 



In imbedding two main things should be looked after : The paraffin should 

 be hot so that it will thoroughly fuse with the paraffin in the tissue. The tissue 

 should be kept from the bottom of the box, either by holding it up in the middle 

 of the box with warmed forceps or a perforated section lifter while a stratum 



*Thickened cedar-wood oil like that for oil immersion objectives is recom- 

 mended by Lee for clearing. This is very expensive, and for most work unneces- 

 sary. Any form of cedar-wood oil has been found satisfactory in the writer's 

 laboratory. The great thing is to have the tissue thoroughly dehydrated before 

 putting it into the oil. 



