ON STAINING FLUIDS, AND STAINING. 113 



the necessary " all round" support to the specimen. 

 The embedding being accomplished, the cylinder is 

 to be driven into the well of the microtome and 

 moistened with alcohol, which will cause the pith 

 cells to swell and firmly enclose and support the 

 specimen, whilst if the cylinder should not already 

 fit into the well with the necessary exactitude this 

 swelling will ensure perfect tightness. 



Wax and Oil. Equal parts of white wax and 

 olive oil are to be melted by heat over a sand bath. 

 In warm weather, or in a hot room, the proportion of 

 wax should be slightly increased ; in colder weather, 

 or in a cool room, increase the proportion of oil. 

 The mass must, of course, be melted when used. 

 The specimens to be embedded should be immersed 

 in alcohol and thoroughly dehydrated, and then 

 placed for a few seconds in collodion, which being 

 allowed to evaporate to dryness, the specimen is 

 then embedded either in the well of the microtome 

 or in a paper tray. The ring of collodion surround- 

 ing the sections will be dissolved away by the clear- 

 ing medium. 



Embedding in Paraffin. The infiltration 

 with paraffin, and subsequent embedding of speci- 

 mens therein, is a process of much nicety and 

 requiring great care, and first, the selection of a 

 suitable paraffin and the composition of the "mass" 

 are all-important. Two paraffins with the different 

 melting-points of 110 F. and 140 F. should be 

 combined in such proportions as shall give a firm 

 and homogeneous mass which, when after melting it 

 has solidified, will cut perfectly smoothly in a tem- 

 perature of from 55 to 70 F. It will be found in 

 practice that two parts of the paraffin of the 140 

 8 



