METHODS OF STAINING. 381 



Method of Mounting Paraffin Sections. 



The student is advised to use for serial sections slides 40 x 76 mm. and 

 from 1.75 to 2 mm. thick. The thick slides are much better than the thin 

 ones recommended by dealers. The cover-glasses ought to be 0.17 to 0.18 mm. 

 thick. A generally convenient size is 35 x 50 mm. 



The serial order of the sections should be preserved with the utmost care, 

 and time spent in arranging the sections in straight rows will be found to be time 

 saved. 



The albumen-glycerin method of fastening the sections to the slide will be 

 found satisfactory. 



Formula: Take the white of one fresh egg, beat slightly until equally fluid, filter it (it will take about 

 twenty-four hours), and add an equal amount of glycerin. To this fluid add a small piece 

 of camphor. 



i.' Clean the slide thoroughly. 



2. Put on a small drop of albumen solution. 



3. Spread it out very thin with the finger. 



4. Add five or six drops of distilled water, which must flow evenly over the 

 coating of albumen. 



5. Place the sections on slides in regular rows. 



6. Warm the slides gently over an alcohol flame, to allow the sections to 

 flatten. The paraffin must not melt. 



7. Drain off the water- as completely as possible, and arrange the sections in 

 straight rows. 



8. Place the slides in oven for twelve to twenty-four hours to evaporate the 

 water completely. 



9. Dissolve off the paraffin in turpentine or xylol. 



10. Put in absolute alcohol for three to five minutes. 



11. Clear in turpentine or chloroform. 



12. Mount in damar varnish. (Canada balsam is undesirable, because it 

 becomes much discolored with age.) 



Methods of Staining. 



In embryological work the specimens are usually stained in toto before im- 

 bedding, either with alum cochineal or with borax carmine, the former being the 

 more generally useful stain. Staining on the slide is also much used either to 

 secure a counterstain after the in toto coloration or to secure some special result. 

 For counterstains eosin, Lyons blue, and orange G are particularly recommended. 

 A few of the most important special stains are given below. 



i. ALUM COCHINEAL. 



Formula: Powdered cochineal 6 gm. 



Potassic alum 6 gm. 



Water .80 c.c. 



