492 DA FANO 



ture from six hours to three days. (4) Treat sections for twenty 

 to thirty minutes with Bielschowsky's ammoniacal silver nitrate 

 solution prepared with only 2 drops of 40 per cent, caustic soda 

 and diluted with re-distilled water to 40 to 70 c.c. (5) Reduce, 

 tone, counterstain, and mount as by Bielschowsky's method for 

 sections. 



Mod, 2 (Proc. Physiol. Soc. J own. Physiol., lii, 1919) consists 

 in an application to nervous tissues of Mod. 1. The use of 

 re-distilled water and the mode of preparing the ammoniacal 

 silver bath are the same, but Da Fano lays stress on the following 

 points : (1) Nervous tissue must be fixed in 10 up to 20 per 

 cent, formalin for at least three weeks, better still for two months. 

 Attempts to obtain a rapid fixation with 10 to 20 per cent, formalin 

 at 37° C. gave bad results. (2) Sections of nervous tissues may 

 be placed, after washing in re-distilled water, in anhydrous 

 pyridine (six to twelve hours), then repeatedly washed and left 

 overnight in re-distilled water, to get rid of all pyridine. This 

 treatment appears to render neurofibrils a little thinner and, 

 consequently, a little sharper, but increases the length and cost 

 of the method, and may cause precipitates to form, especially 

 where much myelin is present. (3) It is possible to keep sections, 

 which cannot be stained immediately, for some days or even a 

 fortnight, in re-distilled water to which a few drops of formalin 

 have been added. Thorough washing w^ith re-distilled water 

 is then imperative before they are transferred into the 2 per 

 cent, silver nitrate solution. (4) Sections of nervous tissues must 

 not remain in the 2 per cent, silver nitrate more than forty- 

 eight hours, or precipitates may form. The longer their stay 

 there, the longer must be the washing before staining ; this, 

 however, must not, as a rule, exceed five minutes. (5) The volume 

 to w^hich the ammoniacal silver nitrate is diluted should be 

 35 to 45 c.c, and the sections remain in it fifteen to twenty 

 minutes. The subsequent washing before transferring the sections 

 into 20 per cent, formalin should not occupy more than ten to 

 fifteen seconds, and their stay in the final formalin solution 

 (especially for cerebral cortex) should not exceed two to three 

 hours. 



The other eight Da Fano modifications {Proc. Physiol. Soc., 

 Journ. Physiol., liii, 1919-20) were all proposed for the study 

 of cortex cerebelli, and are characterised by a special treatment 

 of the sections (cut by freezing method) with various reagents 

 before transferring them into the 2 per cent, silver nitrate solution, 

 nothing having been changed, however, in regard to the long 

 fixation of material in formalin and the use of re-distilled water. 

 They may be summarised as follows : — 



Mod. 3. Place sections, after washing in re-distilled water, in 

 2 to 3 per cent, silver nitrate at 36° to 37° C. for about twenty- 



