294 



PARAFFIN METHOD 



ICH. X 



Nearly fill the box with paraffin wax, ' place on a copper heater 

 (Fig. 241) and allow to remain until bubbles appear in it. Put the 

 box on cold water until a thin stratum of paraffin solidifies on the 

 bottom. Take the piece of tissue from the melted paraffin (Fig. 

 230) and arrange in the box for making sections in a definite direc- 

 tion. Add hot paraffin if necessary, and then place the box on cold 

 water. The more rapid the cooling the more homogeneous will be 

 the block containing the tissue to be cut. For the best imbedding 

 it is well to drop 95% alcohol on the surface as soon as a film has 

 formed in cooling. In warm climates where cold water is not easy 

 to procure for cooling the blocks, one may float the paper box on 

 95,% alcohol and w'ith a pipette (Fig. 240) drop strong alcohol on 

 the sides of the box and on the top of the paraffin as soon as a sur- 

 face film has formed. 



It is very desirable to mark on the box the name of the 

 imbedded object and to indicate which end or face is to be cut. See 

 also under serial sectioning (§ 472-473). 



Fig. 232. Various forms 

 of scalpels. The one at the 

 left is especially excellent for 

 cutting the ribbons of sec- 

 tions of the proper length for 

 mounting. The large one 

 with straight edge is the 

 best form for trimming the 

 paraffin block square for 

 sectioning. {Cut loaned by 

 the Bausch & Lomb Opti- 

 cal Co.) 



§ 442. Fastening the Block to a Holder. — Use one of the 

 block holders or object discs furnished with the microtome, or a 

 short stove bolt (Figs. 233-236). Heat the larger end and press 

 the paraffin block against the hot metal until it melts the paraffin. 

 Hold the two together while cold water flows over them. When 

 cold the block is firmly cemented to the holder. Pains should be 

 taken to have the axis of the block parallel with the long axis of 

 the holder ; and one should not cut the block so short that th,e 

 holder comes in contact with the tissue when the two are cemented 

 together. 



* A clamp is sometimes used for holding the paraffin block (Figs. 

 229, 246-247). 



