10 H. V, NEAL 



is better after months or years. Immediately before use, several 

 drops of this tincture — depending on the strength wanted — are 

 dissolved in distilled water and the sections are stained warm 

 on the slide at 50° C, or for a longer time cold. The sections 

 may be stained directly or they may be mordanted in iron alum. 

 The neurofibrils are differentiated by the Bielchowsky-Paton 

 process but, like the Cajal method, this does not demonstrate 

 the fibrils within the neuroblast cell in the earliest stages of 

 histogenesis. By this method the neurofibrils are stained a dark 

 brown or black, while other tissues are light brown or yellowish 

 brown. In the process only tested distilled water and absolutely 

 clean glass ware and glass or bone spatulas^-no metal — should 

 be used: 



1. Fix and keep embryos in 10 per cent formalin neutralized or made 

 slightly alkaline "v\dth magnesium carbonate. 



2. Wash in running tap-water for twelve hours. 



3. Wash in three or four changes of distilled water for a half-hour. 



4. Place in pure 1 per cent nitrate of silver for six days in the dark 

 at a temperature of about 70°C. Tissues must become reddish-brown 

 in color. If they become yellowish-brown, throw away. 



5. Place in a solution of silver nitrate freshly prepared as follows : 

 20 cc. of 1 per cent silver nitrate. Add 2 drops of 40 per cent caustic 

 soda to form a gray precipitate. Then add 20 to 30 drops of strong 

 ammonia, enough to dissolve the precipitate while stirring. . Allow to 

 remain at least forty-five minutes. 



6. Wash quickly in two baths of distilled water and quickly place 

 in distilled water, to every 20 cc. of which five drops of glacial acetic 

 acid has been added. Leave in this five to fifteen minutes or until 

 the reddish-brown becomes yellowish bro"«ai. 



7. Wash quickly and place over night in 1 per cent hydroquinone 

 containing 5 per cent neutral formol. 



• 8. Wash quickly in distilled water, run up through alcohols rapidly 

 and imbed in paraffin through benzole or chloroform. 



9. Cut sections and fix on slide. Dry well, then paint slides with 

 0.5 per cent celloidin. This is followed by absolute alcohol-xylol, and 

 absolute alcohol-xylol again. Then absolute alcohol to 95 per cent 

 alcohol down to water (distilled) . 



10. Then one to two hours in 0.1 per cent solution of gold chloride 

 neutralized with lithium carbonate. Grubler and Hollborn's gold chlo- 

 ride should be used (flavum, not fuscum), 



11. Rinse in distilled water and fix in 5 per cent hyposulphite of 

 soda for fifteen minutes. Wash in running tap water for two hours. 

 Then alcohols up to absolute. Then absolute and eosin for a minute. 

 Absolute alcohol, xylol, and mounlT in neutral balsam. 



