10 ATLAS OF NERVE CELLS 



this case be dispensed with. The writer found subsequently, but independently, that fresh 

 tissue could be placed immediately in a mixture of formalin and potassium bichromate, and 

 thence brought into the silver nitrate solution. Thus formalin may be substituted for osmic 

 acid, but it has to be used in much larger proportion. 1 



The best proportions for the fluid and periods of hardening for this method have not 

 yet been sufficiently worked out. The addition of from 2\ % to 30% of formalin to 32 % to 



5 % of bichromate, and a period of hardening for 18 hours or upwards, have all been recom- 

 mended. In fact, considerable latitude in both respects appears to be allowable. The results 

 are similar to those of the long Golgi method, which it also resembles in the fact that 

 pieces of impregnated tissue, or sections therefrom, can be left in strong alcohol for a con- 

 siderable period, days or even weeks, without deterioration. It is not improbable that this 

 will prove the best method, when properly developed, for the adult central nervous system of 

 mammals, but it is not as well suited for embryonic tissue as the rapid method of Golgi. 

 Its defect lies in its deficient hardening power. With adult tissue, where the osmic-bichromate 

 mixture penetrates very poorly, and also overhardens the periphery, this defect is an advantage. 

 Another advantage of this method is, that the favourable period for impregnation is not, 

 apparently, passed through so rapidly in the hardening. If brains are injected through the 

 carotid arteries with a solution strong in formalin (e.g. formalin i vol. + potassium bichromate 

 10 % sol. i vol.), the best results of both hardening and subsequent impregnation may be 

 obtained. 



The following table will give further details as to how the majority of the preparations 

 here reproduced were made. By " used " is meant a solution which had been previously 

 used but remained in good condition. As a rule, it is better, however, to use a fresh solution. 

 By " osmic-bichromate " is meant a solution consisting of potassium bichromate 3^ % 4 vols. + osmic 

 acid i % i vol. 



PLATE. HARDENING FLUID ; TIME OF HARDENING. SILVER SOLUTION. 



III., V., & VI. Miiller i wk., osmic-bichromate several days Silver nitrate |% 



VII., VIII., IX., ) (Zinc sulphate 2% i vol. ) 100 cc. -\- 2 drops 



- Berkley's solution (used) 2 da. 20 hrs. 



6 X. ) (Silver nitrate 2% i vol. ) formic acid. 



1 The substitution of formalin for osmic acid in the hardening was first made by the writer during the summer of 1894, 

 and the fact announced in a note to his article "The Cranial Nerves of Amphibia," dated July, 1894, which appeared in the 

 "Journal of Morphology," Vol. X. No. I, January, 1895. A communication was read before the New York Academy of Sciences 

 Jan. 14, 1895, an abstract of which appeared in the " Anatomischer Anzeiger" for March 15, 1895 (Bd. X. No. 15). In the 

 number for June 13, Dung records similar observations, the March number of the "Anreiger" not having come into his hands 

 when his communication was sent off. In the number for July 19, Lachi calls attention to the fact that this mixture was 

 recommended by him in the "Monitore Zoologico," 1895, Anno. VI. No. i, and also by Isola in the "Bullettino della R. 

 Accademia Medica di Genoa," 1895, No. 2, and in the " Gazzetta degli Ospedali," February, 1895. 



