292 



PARAFFIN METHOD 



[OY. X 



The tissue to be cut in this way is first fixed by one of the fixers 

 used for histology. Several good ones are given in sections 406, 

 416, 423, 429. 



(A) The tissue is then thoroughly dehydrated by means of 

 95% and absolute alcohol. For most objects, especially embryos 

 and other colorless objects it is best, during the dehydration, first 

 to use alcoholic eosin ( 402), as the most delicate part shows when 

 one cuts the sections. Leave the piece of tissue to be cut over 

 night in alcoholic eosin, and a few hours in uncolored 95% alcohol 

 using 20 times as much alcohol as tissue. For the final dehydra- 

 tion it should be left in absolute alcohol four or five hours or over 

 night, depending on the size of the object. 



(B) Remove the alcohol by a solvent of the imbedding mass, 

 that is by some substance which is miscible with both alcohol and 

 the imbedding mass ( 422, 441). Cedar wood oil is most generally 

 used ( 390). Leave the tissue in cedar oil until the tissue sinks 

 and the thin parts of the specimen become translucent. If the tissue 

 does not sink after a time it means that the tissue was not dehy- 

 drated. Of course this does not apply to lung or other spongy tissue 

 containing mnch air. It is well to change the cedar oil once. The 

 used cedar oil may be left in an open bottle for the evaporation of 

 alcohol and used over and over again. 



A B 



FIG. 230. Paraffin dish for infiltrating in the Lillie oven. It is made of 

 copper and as shown has a handle for ease in transference. A, the ivhole dish, 

 B, the dish in section. (Jour. Appl. Micr. 1899, p. 266. ) 



(C). Displace the cedar oil by melted paraffin wax. When 

 the tissue is saturated with the oil, transfer it to an infiltrating dish 



