248 GUIDANCE IN MAKING PERMANENT PREPARATIONS 



cohol, or the tissues will continue to bleach after they are 

 mounted. The specimen is now ready for final dehydration. 

 In damp climates, as at the seashore, your stronger alcohols 

 must be kept closely covered all of the time or they will take 

 water from the atmosphere and be unfit for the purpose. 

 Absolute alcohol may be kept from excessive dilution under 

 these conditions by placing in it a fine-mesh cloth bag con- 

 taining anhydrous copper sulphate which must be renewed 

 from time to time. Run through 80 per cent, 95 per cent, 

 and 100 per cent alcohol, thus completing dehydration. 

 Every trace of water must be removed and then kept out. 



Clearing and Mounting. 1 — From absolute alcohol, place 

 objects in some clearing fluid (clove oil, cedar oil, or xylol) 

 and leave till they have a clear, translucent appearance, after 

 which place on a clean slide, with some Canada balsam or 

 damar, and cover with a cover glass. 



If the object turns cloudy or milky when placed in the 

 cleaning fluid, it is evidence that all of the water has not been 

 removed, and it should be returned to absolute alcohol for 

 complete dehydration. Tissues left in the clove oil or xylol 

 for any great length of time will become hard and brittle. 

 In case tissues in the process of preparation must neces- 

 sarily be left untreated for several days, they should be left 

 in a 70 per cent or 80 per cent alcoholic medium. 



Sectioned Material. — In a few cases sectioned material, 



previously stained in toto, may be distributed to the class. Be 



sure that the slide on which you intend mounting the sections 



is thoroughly clean. Remove any greasy substance with 95 



per cent alcohol. On a cleaned slide, smear a very little 



albumen fixative with your fingertip and remove all except 



the thinnest film. On water placed over this film of albumen 



float the sections. Very gently heat the water until the sec- 



1 Specimens may be successfully mounted in euparal from 95 per 

 cent alcohol. This avoids labor of dehydration and clearing and gives 

 permanent mounts. For total mounts of parapodia, etc., methyl salic- 

 ylate (synthetic oil of wintergreen) may be used to clear directly 

 from 95 per cent alcohol. 



