432 NERVOUS SYSTEMSPECIAL METHODS. 



uses again 20 per cent, formaldehyde. To avoid an excessive im- 

 pregnation of the connective tissue he also finds it useful to wash 

 pieces in acidified distilled water (see the Bielschowsky method for 

 peripheral nerve-fibres), but he uses as much as five times the 

 amount suggested by Bielschowsky. 



842. DA FANG'S Modifications. An important point of this 

 series of modifications of Bielschowsky 's method for sections is 

 the use of distilled water, re-distilled on potassium permanganate, 

 with the object of ensuring elimination of any trace of organic 

 matter from the ordinary distilled water and of avoiding the forma- 

 tion of precipitates. 



Da Fano's first modification (Mod. 1) (Atti. Soc. Lomb. Sc. Med. 

 BioL, Milano, iii, 1914) was meant for the study of recticular tissue 

 of spleen, lymph glands, and other organs, and is to be carried out 

 as follows : (1) Fix small pieces of fresh tissue in 10 to 20 per cent, 

 formalin or in Kayserling's first fluid (forty-eight hours at least), or 

 in Orth's fluid (twenty-four to forty-eight hours). (2) Wash pieces 

 in running tap-water for twenty-four to thirty hours, and then in 

 distilled water for another twenty-four hours. (3) Wash sections 

 made by the freezing method in re-distilled water (twenty-four 

 hours), and then place them in filtered 2 per cent, silver nitrate 

 (prepared with redistilled water) in a Petri dish, taking care that 

 they do not touch each other. Here they are kept in the dark and 

 at room temperature 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 redistilled \vater to 40 

 to 70 c.c. (5) Reduce, tone, counterstain, and mount as by Biel- 

 schowsky's method for sections. 



Mod. 2 (Proc. Physiol. Soc. Journ. Physiol., Hi, 1919) consists in 

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

 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 redistilled water, in anhydrous pyridine (six to 

 twelve hours), then repeatedly washed and left overnight in redis- 

 tilled water, to get rid of all pyridine. This treatment appears 

 to render neurofibrils a little thinner and, consequently, a little 



