NEUROFIBRILS 483 



acidifying the fixatives. He takes : {a) 25 per cent, formol with 

 5 per cent, of acetic acid ; or (6) the same with 0-5 per cent, of 

 ammonia ; or (c) 100 c.c. of alcohol, 25 c.c. of formol, 5 c.c. of 

 acetic acid, and 0-5 c.c. of ammonia. For the impregnation he 

 uses 3 per cent, silver nitrate with 15 per cent, of alcohol, and 

 reduces in the usual hydroquinone-formol solution, with the 

 addition of 15 c.c. of alcohol. These results are confirmed by 

 KowALSKi {La Cellule, xxv, 1909, p. 292, and by Szuts {Anat. 

 Anz., xlii, 1912, p. 262). Kowalski gets impregnations also by 

 simply starving worms for several days, or exposing them to 

 cold (—5° C.) for a quarter of an hour. 



9. Regenerating nerve-tissue. For nerves operated on a month 

 or more previously, Formula 2 or 3, with not more than 3 drops 

 of ammonia, will stain equally the old and the new fibres ; for 

 nerves operated on not more than two to ten days previously. 

 Formulae 3 with 4 to 6 drops of ammonia, 5 with pyridin, and 4, 

 also sometimes 6 ; for regeneration in cord, cerebrum, and cere- 

 bellum, 3 with 3 drops of ammonia, or 5, or pure alcohol. 



1013. Modifications of Ramon y Cajal's Methods. Da Fang 

 (Ziegler's Beitr., xliv, 1908, p. 495) recommends using solutions of silver 

 nitrate and hydroquinone in 1 : 10,000 gelatin in order to obtain a 

 deeper and sharper impregnation. 



Kato {Folia neurobiol., ii, 1908, p. 262) fixes in 10 to 15 per cent, 

 formol, and silvers for one to five days at 35° C. in 5 per cent, argentamin 

 to which 3 per cent, of silver nitrate has been added in such a way as 

 to have an impregnating fluid with a little argentamin in excess ; or 

 argentamin 8 to 10 parts, with 3 per cent, potassium bichromate 30 

 parts and distilled water 100 parts. For the reduction he uses 10 per 

 cent, formol with 1 per cent, hydroquinone. 



PusATERi (see Amato, Virchow's Arch., clxxxv, 1908, p. 547) fixes 

 for three to six days at 35° to 38° C. in a mixture of 45 c.c. of tachiol 

 (10 per cent, silver fluoride) and 155 of distilled water. 



Besta (Riv. pat. nerv. ment. Firenze, xv, 1910, p. 333) fixes for forty- 

 eight hours in alcohol with 5 per cent, nitric acid, neutraUsed in alcohol 

 with ammonia. 



LiESEGANG (Kolloidchemie Beihefte, iii, 1911, H. 1, p. i ; Ztschr. wiss. 

 Mikr., xxviii, 1912, p. 369) makes sections of formol material by the 

 freezing method, and puts them in 1 per cent, silver nitrate in the dark 

 for hours or days imtil yellow. If necessary, increase the strength of the 

 silver solution or place the dish in the incubator. Pour off the silver 

 solution with the exception of about 2 c.c. ; add equal parts of 50 per 

 cent, gum and of a concentrated solution of hydrogen potassium 

 sulphide. Wash in distilled water and mount in the usual way in 

 balsam. 



AscoLi {Boll. Soc. med. chir., Pavia, 1911, p. 177) recommends for 

 the nervous system of Hirudinea the following : The animals cut open 

 at the back are stretched on a piece of cork and fixed in a solution 

 prepared by dissolving over a flame 5 gr. of pulverised crystals of 

 silver nitrate in 100 c.c. of 95 per cent, alcohol. After a few minutes 

 the animals may be detached from the cork and put back in the same 

 fixative for twenty-four to forty-eight hours in an incubating stove. 

 They are then transferred for another twenty-four to forty-eight hours 

 into a 10 per cent, watery solution of silver nitrate, to be kept also in 



16—2 



