NERVOUS SYSTEM. 41 3 



neuroglia cells ; three to five days for nerve cells ; five to 

 seven days for collaterals). The pieces of tissue are transferred 

 to 0.75 per cent, silver nitrate solution after having being 

 washed in water and dried with filter- paper. They are left at 

 ordinary room temperature in the silver nitrate for from two 

 to three days. At this point a precipitate of silver chromate 

 often forms, in which case the whole proceeding must be repeated. 

 The pieces are then transferred to absolute alcohol for from 

 one-half to one hour and imbedded quickly in celloidin i. e., 

 thirty minutes. Comparatively thick sections are cut, dehy- 

 drated in absolute alcohol (two minutes), cleared in oil of 

 bergamot, and mounted without a cover glass in balsam. The 

 best results with the nervous system are obtained with embry- 

 onic tissues. 



59. For all kinds of nerve-endings the gold chloride method 

 of Ranvier and its many modifications may be used. Tissue 

 is placed in a mixture made by boiling 8 parts of 1 per cent, 

 gold chloride solution with 2 parts of formic acid. After an 

 hour's action in the dark the tissue is washed in distilled water 

 and allowed to remain in 20 per cent, formic acid in daylight 

 for from twenty-four to forty-eight hours. It is then hardened 

 in alcohol and imbedded in celloidin. Many other methods 

 have been employed with success (e. g., filtered lemon-juice five 

 minutes, 1 per cent, gold chloride 1 hour, lemon-juice twenty- 

 four hours ; or formic acid 1 per cent, for one hour, gold 

 chloride 1 per cent, two hours, formic acid 10 per cent, 

 twenty-four hours). In none of these methods should metallic 

 instruments be used. Instead of being sectioned, the tissue 

 may sometimes (e. g., muscle) be teased out in glycerin. 



60. Nerves and nerve-endings may also be demonstrated 

 by staining them with methylene-blue (Ehrlich), in one of the 

 following ways : 0.33-4 per cent, solution of methylene-blue 

 in warm physiological salt solution is injected into the veins 

 (external jugular) of an animal. After a few hours the sympa- 

 thetic ganglion cells, muscles, etc., are examined. Another 

 method is to cut thin sections ( 5-1 mm. thick) of tissue from 

 an animal which has just been killed, and stain this fresh tissue 



