STAINING REAGENTS. 79 



dark. Wash it thoroughly with water, and mount in glycerine or 

 balsam. 



3. Ranvier's Lemon-Juice Method. The fresh tissue is placed 

 for c^io minutes in the freshly expressed and iiltered juice of a 

 lenion, until it becomes transparent. Rapidly wash it in distilled 

 water, transfer it to i per cent, gold chloride solution for from ten 

 minutes to one hour; the time depends on the tissue under investi- 

 gation. Wash with water and place the tissues in 50 cc. of water 

 containing two drops of acetic acid, and expose them to light, when 

 reduction takes place. Or the tissue may be placed in formic acid 

 (1:3) after being treated with lemon-juice and gold chloride, and 

 kept in the dark for twenty-four hours. The latter plan is in many 

 cases to be preferred, especially where the retention of the super- 

 ficial epithelium is not desired. 



4. Boiled Gold Chloride. For some purposes, especially for 

 studying the terminations of the nerves in sensory surfaces, this 

 method of Ranvicr has yielded me the best results. 



Make as required fresh a mixture of four parts of gold 

 chloride (i per cent.) and one part of formic acid. Boil the 

 mixture and let it cool. Place the fresh tissues (small pieces) in it 

 for ten minutes to one hour. Wash in water, and place in formic 

 acid (1:4 water), and keep in darkness, where the reduction 

 takes place. 



5. Rapid Reduction of Gold Chloride. A tissue may be left in 

 gold chloride (i per cent.) for half-an-hour or more, and then trans- 

 ferred to a strong solution of tartaric acid and heated to 45 or 50 

 C., when it rapidly becomes of a purplish-brown colour, usually in 

 the course of a quarter of an hour. 



Although it has been stated that for gold chloride preparations 

 the tissues should be fresh, Drasch, in his researches on the nerves 

 of the intestine and those of the circumvallate papillae, points out 

 that he obtained the best results with tissues twenty-four hours 

 after death ; the tissues, however, must have been kept cool. Any 

 one who has had the privilege of studying the preparations of 

 Drasch cannot but have been impressed with the beauty of speci- 

 mens prepared by his method. 



6. Gold Chloride and Chromic Acid (Kolossow). Place the 

 tissues for 2-3 hours, according to their size, in i per cent, gold 

 chloride acidulated with hydrochloric acid (i-ioo). Wash the 

 tissues with water, and keep them in the dark in chromic acid 

 (5*0 ^ wo P er cen k) f r 2 ~3 days. Wash out the chromic acid 

 thoroughly. 



7. Method of Ciaccio is good for the termination of nerves in 

 cornea and muscles. Place a small piece of tissue, not more than 2 

 cubic mm. in size, in fresh juice of lemon (5 minutes) : wash ; place in 



