METALLIC STAINS (IMPREGNATION METHODS). 221 



then made and mounted in dammar or glycerin. Successful 

 preparations show the nerves alone stained. 



365. RANVIER'S Formic Acid Method (Quart. Journ. Mic. Sci. 

 [N.S.], Ixxx, 1880, p. 456). The tissues are placed in a 

 'mixture of chloride of gold and formic acid (four parts of 1 

 per cent, gold chloride to one part of formic acid) which has 

 been boiled and allowed to cool (RANVIER'S Traite, p. 826). 

 They remain in this until thoroughly impregnated (muscle 

 twenty minutes, epidermis two to four hours) ; reduction is 

 affected either by daylight in acidulated water, or in the 

 dark in dilute formic acid (one part of the acid to four parts 

 of water). 



366. RANVIER'S Lemon-juice Method (Traite, p. 813). 

 RANVIER finds that of all acids lemon juice is the least hurt- 

 ful to nerve-endings. He therefore soaks pieces of tissue in 

 fresh lemon juice until they become transparent (five or ten 

 minutes in the case of muscle). They are then rapidly 

 washed in water, brought for about twenty minutes into 1 

 per cent, gold chloride solution, washed again in water, and 

 brought into a mixture of 50 c.c. of distilled water and two 

 drops of acetic acid. They are exposed to the light for 

 twenty-four to forty-eight hours. The preparations thus 

 obtained are good for immediate study, but are not permanent, 

 the reduction of the gold being incomplete. In order to 

 obtain perfectly reduced, and therefore permanent, prepara- 

 tions, the reduction should be done in the dark in a few cubic 

 centimetres of dilute formic acid (1 part acid to 4 of water), 

 which takes about twenty-four hours. 



- 



367- VIALLANE'S Osmic Acid Method (Hist, et Deo. des 

 Insectes, 1883, p. 42). The tissues are treated with osmic 

 acid (] per cent, solution) until they begin to turn brown, 

 then with 25 per cent, formic acid for ten minutes ; they are 

 then put into solution of chloride of gold of 1 : 5000 (or even 

 much weaker) for twenty-four hours in the dark, then reduced 

 in the light in 25 per cent, formic acid. I find this an ex- 

 cellent method. 



KERSCHNER (Arcli. mik. Anat., Ixxi, 1908, p. 522) puts till 

 brown into a mixture of ten parts 5 per cent, formic acid 



