CH. VII] PARAFFIN SECTIONING 183 



\ 281. Mounting in Balsam. — After the sections are stained they must be 

 dehydrated and cleared before mounting in balsam. For the dehydratiou the slide 

 is plunged into a jar of 95% alcohol. For clearing after the dehydration the slide 

 is drained of alcohol and put down flat and the clearer poured on, or the whole 

 slide is immersed in a jar of clearer (\ 318). Clearing usually is sufficient in a 

 few minutes ; a stay of an hour or even over night does not injure most sections. 



In mounting in balsam the clearer is drained away by standing the slide nearly 

 vertically on some blotting paper, or by using the waste bowl and standing it up 

 in the little funnel (Fig. 148). Then the balsam is put on the sections or spread 

 on the cover-glass and that placed over the sections. 



For cataloging and labeling, see $ 307-310. 



Fig. 153. Small spirit lamp modified into a bal- 

 sam bottle, or a glycerin or glycerin-jelly bottle, or a 

 bottle for homogeneous immersion liquid. For all of 

 these purposes it should contain a glass rod. See also 

 Fig. 16S. 



\ 2S2. The Collodion Method with Alcohol.— A good method of procedure 

 for making collodion sections is to do exactly as described, including \ 272, and 

 then instead of hardening the collodion in chloroform and clarifier, it is hardened 

 in 82% alcohol for a day or two before sectioning. In sectioning the knife and 

 tissue are kept wet with 82% alcohol and the sections are dehydrated with 95% 

 alcohol and then fastened to the slide with ether alone or with ether-alcohol. 

 The staining and mounting (? 278-281) are as described. One may preserve the 

 tissue after imbedding for a long time in the 82% alcohol before sectioning and 

 sections may be made at any time. While this method appears somewhat simpler, 

 the results are not so satisfactory as by the oil method given above. 



THE PARAFFIN METHOD 



§ 283. As with the collodion method, the tissues are first properly fixed and 

 hardened and then entirely filled with the imbedding mass, but unlike the collo- 

 dion the mass must be entirely removed before the sections are finally mounted. 

 The tissue thus imbedded and infiltrated is like a homogeneous mass and sections 

 may be cut of extreme thinness. 



\ 284. Harden perfectly fresh tissue in picric-alcohol ($ 333) 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 



