CHAPTER XXXIV. 463 



cent, potassium bichromate, filtering them if copper acetate was 

 used, and treating the pieces as stated above. As a rule these copper 

 acetate and potassium bichromate mixtures ought to be tried first 

 and in preference to others. As with other points of Golgi's methods, 

 so also in this case, one must proceed by tentative experiments, 

 according to the purpose of one's investigation and the quality of the 

 material in hand, but chiefly according to the length of time during 

 which the tissues have been left in the osmio-bichromate solution. 



See on this subject SACERDOTTI, Intern. Monatschr. Anat., xi, 1894, 

 p. 326 ; GOLGI, Cinquant. Soc. Biol., 1899, p. 514, and Opera Omnia II, 

 1903, p. 677 ; FUSARI, Trait. Elem. Istol. Teen. Istol, Torino, 1909 ; 

 SALA G., Anat. Anz., xviii, 1900, p. 176 ; GEMMELLI, Anat. Anz., 1913, 

 p. 444. 



889. Formaldehyde Modifications of GOLGI' s Bichromate and Nitrate 

 of Silver Method. Many investigators have found that formaldehyde 

 can take the place of the osmic acid in the osmio-bichromate 

 mixture of the rapid process. This has certain advantages : A 

 cheap reagent is employed instead of the expensive osmic acid. 

 Pieces much larger than by Golgi's original process may be used. 

 The stage of hardening favourable for a good impregnation lasts 

 longer, i.e., formalin-bichromate mixtures do not over-harden. 

 Moreover, the formaldehyde modifications can be usefully resorted 

 to for impregnating nervous tissues of adult or young subjects, as 

 well as for material which after repeated attempts has been found 

 impervious to the osmic mixtures. However, it should be remem- 

 bered that many investigators have failed to obtain good results 

 by the formaldehyde methods and that they are unsuitable for 

 embryonic specimens. 



HOYER, Jun. (Anat. Anz., ix, 1894, p. 236) was the first to point 

 out that material fixed in formalin could be used for carrying out 

 Golgi's method. 



LACHI (Monit. Zool. ItaL, v, 1895, p. 15) used, at first, to harden 

 tissues for five to nine days in equal parts of 20 per cent, formalin 

 and 6 per cent, potassium bichromate. Afterwards (Anat. Anz., 

 x, 1895, p. 790) he adopted the mixture proposed by his pupil 

 DELL'ISOLA (Boll. Ace. Med. Genova, 1895. No. 2) of equal parts of 

 10 per cent, formalin and 10 per cent, potassium bichromate, with 

 the addition of 1 part of 1 per cent, osmic acid to every 10 of the 

 mixture, this last formula being particularly suitable for quick work, 

 as forty-eight hours afterwards pieces can be already transferred 

 into the silver bath. 



STRONG (Anat. Anz., x, 1895, p. 494) suggested fixing pieces of 



