654 TECHNIQUE 



the surface of the water ; and the slide is gently heated over a 

 small flame. Thus the parafin sections are straightened ; care 

 should be used not to melt them. The excess of water is now 

 carefully poured off and the slide placed in an oven and heated to 

 about 40 C. for several hours, until thoroughly dried. Most tis- 

 sues will now adhere firmly to the slide. If, however, the tissue 

 was fixed with solutions containing bichromate of potassium the 

 sections are liable to come off the slide, a misfortune which may be 

 avoided by the use of a celloidin adhesive, with or without the 

 previous use of Mayer's albumin. 



Mayer's Albumin : 



White of egg, chopped with scalpel or 



scissors, and filtered 10 cc. 



Glycerin 10 cc. 



Thymol a small crystal. 



A drop of this fluid is to be diluted with eight or ten drops of 

 distilled water and spread with a glass rod upon the surface of a 

 clean slide. The excess is drained off, the slide inverted, leaned 

 against the wall to protect it from dust, and allowed to dry in the 

 air. The parafin sections are now placed upon the slide by the 

 method detailed above. 



Celloidin Adhesive. The sections, having been fastened to the 

 slide and dried, the parafin is removed by dipping the slide into 

 one or two changes of pure xylol, the xylol removed by washing 

 with absolute alcohol, and a few drops of very thin solution of 

 celloidin (made by diluting thin celloidin, number I,* with eight 

 or ten volumes of the alcohol and ether solvent) are poured over 

 the sections. The solution of celloidin should be so thin as to 

 scarcely leave an appreciable film on the slide. The excess of cel- 

 loidin is drained off and the film hardened by first flooding the slide 

 with 70 per cent, alcohol, and after a few minutes transferring it 

 to water. The sections will not now be removed from the slide 

 except by mechanical violence. 



Celloidin sections do not need to be fastened to the slide before 

 being stained ; they are sufficiently firm to be gently handled with 

 a needle. 



Staining in Bulk. It is occasionally desirable to stain tissue in 

 bulk so that sections once cut can be immediately mounted. This 

 is best accomplished by the use of a single stain applied to small 

 blocks of tissue immediately after dehydration. Borax carmin is 



* See page 650. 



