268 PREPARATION OF SECTIONS 



pure acid with very hard woods, to remove silicious deposits that 

 add much to the difficulty of sectioning. After this wash out the 

 acid completely and put the material for several days into equal 

 parts of 30 per cent, alcohol and glycerine preparatory to starting 

 in 90 per cent, alcohol on the way through celloidin, as above 

 described. The hydrofluoric acid solutions must, of course, be 

 used in a dish coated with paraffin. 



Sectioning Celloidin Material. Clamp the block in right 

 position in the object carrier of a sliding microtome (Fig. 143), 

 set the knife slanting so that a long gliding cut will be made, 

 wet the knife with the alcohol-glycerine mixture, and proceed to 

 cut the sections as thin as they can be made; but hope not 

 for success if the knife is dull. With a camel's-hair brush 

 sweep the sections from the knife into a dish of 70 per cent, 

 alcohol. 



Staining Celloidin Sections. Transfer the sections from 

 the 70 per cent, alcohol to the safranin solution described under 

 the three-color method (page 264), and after ten hours or longer 

 rinse them in 70 per cent, alcohol containing one drop of con- 

 centrated hydrochloric acid for every fifty cubic centimeters, 

 until the safranin is very faint in the celloidin but still of suffi- 

 cient intensity in the subject itself. Then pass the sections 

 quickly through 95 per cent, alcohol and transfer them to a 

 mixture of equal parts of bergamot oil, cedar oil, and carbolic 

 acid where they will be further dehydrated and cleared, and 

 then they are ready for mounting in Canada balsam. 



Safranin and Delafield's haematoxylin combine well for 

 double staining celloidin sections. To make the haematoxylin 

 solution dissolve one gram of haematoxylin in 6 c.c. of abso- 

 lute alcohol and add this drop by drop to 100 c.c. of a satu- 

 rated aqueous solution of ammonia alum. Leave this exposed 

 to light and air for one week, then filter it and add 25 c.c. each 

 of glycerine and methyl alcohol and after five hours filter again. 

 Let this ripen about two months before using. 



To double stain the celloidin sections place them in safranin 

 for a day, rinse them in 50 per cent, alcohol, put them into 



