376 



PREPARATIONS BY THE PARAFFIN METHOD [Ch. XI 



§ 611. Infiltration of the tissue with imbedding mass. — The tissue 

 to be cut in this way is first fixed by one of the fixers used for his- 

 tology. Several good ones are given in sections 568, 586, 592, 601. 



(A) The tissue is then thoroughly dehydrated by means of 95 % and 

 absolute alcohol. For most objects, especially embryos and other 



colorless objects, it is best, during the de- 

 hydration, first to use dilute alcoholic eosin 

 (§ 562), as the most delicate part shows when 

 one cuts the sections. Leave the piece of 

 tissue to be cut overnight in alcoholic eosin, 

 and a few hours in uncolored 95 % alcohol, 

 using 20 times as much alcohol as tissue. 

 For the final dehydration it should be left 

 in absolute alcohol four or five hours or over- 

 night, depending on the size of the object. 

 (B) Remove the alcohol by a solvent of 

 the imbedding mass; that is, by some sub- 

 stance which is miscible with both alcohol 

 and the imbedding mass. Cedar-wood oil 

 is most generally used, but pure xylene, 

 chloroform, and carbol-xylene are also used, 

 — the chloroform and carbol-xylene when 

 osmic acid fat is to be retained in the tissue. 

 Leave the tissue in cedar oil or other 

 clearer until the tissue sinks and the thin 

 parts of the specimen become translucent. 

 If the tissue does not sink after a time it 

 means that the tissue was not dehydrated. 

 Of course this does not apply to lung or other spongy tissue contain- 

 ing much air. It is well to change the cedar oil or other clearer 

 once. The used cedar oil may be left in an open bottle for the 

 evaporation of alcohol and used over and over again. 



(C) Displace the cedar oil or other clearer by melted paraffin wax. 

 When the tissue is saturated with the oil transfer it to an infiltrating 

 dish (fig. 220) containing melted paraffin. Place in a paraffin oven 

 (fig. 220) and keep the paraffin melted for from two hours to three 



Fig. 219. Kingsbury's 

 Paraffin Melting Oven. 



(From the Anatomical 

 Record). 



1 Upper part of the 

 oven containing the covered 

 pitcher for the paraffin. 



2 Lower part contain- 

 ing the incandescent lamps 

 and supply cable (c). The 

 oven is well insulated by 

 asbestos. Depending on 

 the temperature of the 

 room, one or both lamps 

 can be used to keep the 

 paraffin melted. 



