1 84 



PARAFFIN SECTIONING 



[_CH. VII 



for each method. The time might be longer or shorter than for the picric-alcohol. 

 (See Lee, the Microtomists' Vade-Mecum.) 



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, and it may remain indefinitely. 



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



\ 285. 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. 143.) 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% is used one will succeed, 

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



FIG. 154. Copper pail with 

 water bottom for melting para- 

 ffin. This also serves as a water 

 bath for large bottles in which 

 saturated solutions of dichro- 

 mate and other salts are pre- 

 pared. 



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

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

 sections may be made. ) 



\ 286. Displacing Alcohol and Clearing Tissues with Cedar-wood Oil and 

 Infiltrating with Paraffin. (Lee, p. 66. Neelson and Schiefferdecker, Arch, fur 

 Anat. und Physiol., 1882, p. 206.) When the tissue is dehydrated it is removed 

 to a vial of cedar-wood oil. When the alcohol used for dehydration is displaced 

 by the oil, the tissue will look clear and translucent. This requires 2 to 24 hours. 



