SECTION CUTTING 11 



is often very useful, as it combines the advantages of both 

 reagents. 



6. Picric Acid is a very valuable hardening reagent, of which 

 the best preparation is Kleinenberg's. Specimens should be left 

 in it from 12 to 24 hours. It is prepared thus : with 100 c.c. 

 of water make a cold saturated solution of picric acid : add 2 

 c.c. of concentrated sulphuric acid : filter, and add to the filtrate 

 three times its volume of water. 



VII.— ON SECTION CUTTING. 



Many tissues and organs can only be studied satisfactorily by 

 cutting them into thin sections, and this method of investiga- 

 tion is of such importance as to require special notice. There 

 ai'e three chief stages : Hardening, Imbedding, and Cutting, 

 which will be noticed in succession. 



A. Hardening. 



Before the object can be cut into sections it is necessary to 

 harden it ; this may be efiected by freezing, but the more usual 

 plan is by means of reagents, which have been discussed under 

 the previous heading. 



B. Dehydration. 



Specimens that have been hardened in any of the preceding 

 reagents, except alcohol, should, on removal, be placed for a few 

 hours in 30 per cent, alcohol, and then transferred to 50 per 

 cent, alcohol : on the following day they should be transferred 

 to 70 per cent, alcohol, which should be changed daily until the 

 specimens are free fi'om the hardening reagent : they may then 

 be left in 70 or 90 per cent, alcohol until required. 



C. Staining. 



The hardened specimens, if not too large, may now be stained 

 with either hsematoxylin, borax-carmine, or picro-carmine ; they 

 should then be replaced in 70 or 90 per cent, alcohol. If the 

 specimen is too large to stain whole, the sections must be 

 stained after they are cut. 



D. Imbedding. 



The preparation of sections is greatly facilitated by imbedding 



