RANVIER' s LEMON-JUICE METHOD. 115 



208. Ranvier's Formic Acid Method (Quart. Journ. Mic. Sci. 

 (N.S.), Ixxx (1880), p. 456). The method of Lowit has been 

 modified by many workers by omitting the final treatment 

 with undiluted formic acid, and also in some other details. 

 Ranvier proceeds as follows. Reflecting that the action of 

 the one-third formic acid in which Lowit placed his tissues 

 must be hurtful to the finer ramifications of the nerves, he 

 combines the formic acid with a fixing agent designed to 

 antagonise its altering action, and takes for this purpose the 

 chloride of gold itself. The tissues are placed in a mixture 

 of chloride of gold and formic acid (4 parts of 1 per cent, gold 

 chloride to 1 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) ; the reduction of the gold is 

 effected either by the action of daylight in acidulated water, 

 or in the dark in dilute formic acid (1 part of the acid to 

 4 parts of water) . 



The object of boiling the mixture of gold chloride and 

 formic acid is this, that " by boiling in the presence of the 

 acid the gold acquires a great tendency to reduction, and for 

 this reason its selective action on nervous tissues is enhanced." 



209. Ranvier's Lemon-juice Method (Traite, p. 813). Instead 

 of combining the formic acid with gold chloride in order to 

 mitigate its action, recourse may be had to a less injurious 

 acid than formic acid. Ranvier finds that of all acids lemon- 

 juice is the least hurtful to nerve-endings. He therefore soaks 

 pieces of tissue in fresh lemon-juice filtered through flannel, 

 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 solu- 

 tion, washed again in water, and brought into a bottle con- 

 taining 50 c.c. of distilled water and 2 drops of acetic acid. 

 They are exposed to the light, and the reduction is complete 

 in twenty-four or forty-eight hours. The preparations thus 

 obtained are good for immediate study, but are not permanent 

 on account of their over-blackening with time, the reduction 

 of the gold being incomplete. In order to obtain perfectly 

 reduced, and therefore permanent, preparations, the reduction 

 should be done in the dark in a few cubic centimetres of dilute 



