130 SPECIFIC EXAMPLES OF SLIDE-MAKING 



the low power of the microscope will show these preparations to have dull 

 purple muscle tissue and intensely blue connective tissue. A few trial sections 

 should now be returned to absolute alcohol for a few moments, put back 

 into xylene, and then reexamined. It is possible by this means to exercise the 

 most perfect control over the differentiation, which should be stopped when 

 the muscles and nuclei are clear red and the connective tissues are a clear 

 light blue. No attention should be paid, while differentiating, to any of the 

 structures, such as the gonad, which by this method acquire a violet coloration 

 which cannot be judged; the process should be controlled only by apparent 

 contrast between the pure blues and pure reds in the section. 



The stains used in this preparation are alkali sensitive, and it is a customary 

 procedure in Europe to mount them in as acid a medium as possible. If one is 

 using one of the synthetic resins, which are neutral, it is strongly recommended 

 that the coverslip, before it is applied to the resin, should be dipped briefly in 

 a strong solution of salicylic acid in xylene. This salicylic acid will dissolve 

 in the resin and provide a permanently acid medium; with this precaution, 

 the sections are permanent. 



Summary 



L Fix a small adult Amphioxus in any good fixative. If only a Bouin-fixed 

 specimen is available, soak it overnight in 1 per cent nitric acid. 



2. Cut 10- M paraffin sections in the usual way, attach to slide, and grade 

 to water. 



3. If fixative does not contain mercuric chloride, soak sections overnight in a 

 saturated solution of this salt and wash for some hours in running water. 



4. Stain in 1 per cent acid fuchsin for about 2 minutes. 



5. Rinse quickly in distilled water and transfer to 1 per cent phosphomolyb- 

 dic acid until no more color comes away (about 2 minutes). 



6. Rinse quickly and place in Mallory's oxalic acid-methyl blue-orange G mix- 

 ture for 15 minutes. 



7. Wash thoroughly in water. Rinse in 95 per cent alcohol to remove adherent 

 water. Differentiate each slide individually in absolute alcohol. Stop differ- 

 entiation with xylene and mount in balsam. 



