CHAP. I '//.] PARAFFIN SECTIONING. 165 



from one to three days. (Any good method for fixing and hardening 

 the elements may be used. One must observe in each case, however, 

 the special conditions necessary for each method. The time might be 

 longer or shorter than for the picric-alcohol. See Lee, the Microtomists' 

 Vade-Mecnm. ) 



If picric-alcohol is used, pour it off after the proper time for fixing 

 has elapsed, and add 67 '/< alcohol. Leave this on the tissue from one 

 to three days, and if it becomes very yellow it is well to change it two 

 or three times. After two or three days pour off the 67^ alcohol and 

 add 82%. The tissue should remain in this one or two days, audit 

 may remain indefinitely. 



In case the alcohol becomes much yellowed, it should be changed. 



\ 270. Dehydration and Preparation for Imbedding- — From the pieces of 

 tissue fixed and hardened in any approved manner, cut pieces 5 to 10 millimeters 

 long and 2 to 3 millimeters in breadth. Place one or two pieces in a shell vial 

 (Fig. 132) and add 95% alcohol. Change the alcohol after two or three hours, 

 and within 6 to 24 hours, depending on the size of the piece to be dehydrated, the 

 dehydration will be completed. The secret of success is the use of plenty of 

 alcohol and sufficient time. Absolute alcohol for the second change would act 

 more promptly and efficiently, but if plenty of 95 ( / r is used one will succeed, unless 

 the day, or the climate in general, is too damp. 



(If one is studying organs, then the whole organ may need to be prepared for 

 imbedding, but for the minute structure small pieces are preferable, as thinner 

 sections may be made. ) 



§ 271. Displacing the Alcohol and Clearing Tissues with Thickened 

 Cedar-wood Oil and Infiltrating with Paraffin. — (Lee, p. 66. Neelson and 

 Schiefferdecker, Arch, fiir Anat. und Physiol., 1882, p. 206.) When the tissue is 

 dehydrated it is removed to a vial of thickened cedar-wood oil. When the alcohol 

 used for dehydration is displaced by the oil, the tissue will look clear and trans- 

 lucent. This requires 2 to 24 hours. 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. 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. 



§ 272. Imbedding in Paraffin. — Make a small paper box, fill it about half full 

 of pure melted paraffin of the proper melting point ( see {5 2711, and then remove the 

 tissue from the infiltrating oven, place it in one end of the paper box and arrange 

 it so that sections may be made in any desired direction. As soon as the paraffin 

 has solidified on the surface, place the box in cold water, on ice or in snow to cool 

 the paraffin quickly, and thus avoid spaces around the tissue, etc. 



§ 273. Cutting the Sections. — After the imbedding mass is well cooled, remove 

 the paper box and trim the end containing the tissue in a pyramidal form. Clamp 



