STAINING AND HARDENING. 237 



itlum logwood, be immersed in an exceedingly dilute 

 bichromate solution, the purple will be replaced by a 

 yellow tint. It therefore follows that sections har- 

 dened in chromic acid solutions, will not colour nearly 

 so readily as if immersed in the fresh state. But it 

 has been found that this objection may be overcome if 

 the sections are well washed and immersed in a modi- 

 fied solution of logwood. The most practical form is 

 made as follows : Take of logwood extract 6 parts ; 

 alum, 6 parts ; sulphate of copper, 1 part ; water, 

 40 parts. All ingredients must be free from iron. 

 Grind up the powders together in a mortar, and 

 when powdered add water sufficient to form a thin 

 paste ; put them by and leave them for a day or two 

 in this state, then add the rest of the water and filter 

 the solution. The hoematein will be separated and left 

 behind in the filter ; and a crystal of thymol may 

 be added to preserve the solution from moulding. For 

 chromic hardened tissues, dilute 8 drops of the fluid 

 with 120 of water, and add one drop of a one-tenth 

 per cent, solution of bichromate of potash just before 

 using the solution. Wash the stained tissues as usual 

 in water, and mount in glycerine, Warrant's solution, 

 or dammar. In the former they keep best, in the last 

 they are apt to fade, unless the sections be thoroughly 

 freed from water by being immersed in absolute alcohol, 

 before being brought into contact with oil of cloves. If 

 any moisture be left behind, the preparations will be 

 sure to spoil. 



A modified Warrant's solution may be prepared as 

 follows : Take of gum arabic 5 parts ; water, 5 parts ; 

 when the gum is fairly dissolved add 10 parts of a five 

 per cent, solution of carbolic acid. 



Hardening, Preserving, and Section-cutting. What- 

 ever be the hardening or softening fluid employed (for 

 this is necessary when bone is the structure about to 

 be examined), its bulk should be large in proportion 

 to the size ; half a pint of fluid for a piece of about 

 one cubic inch. The strength of the fluid must be 

 made to suit the tissue about to be acted upon, and 

 the fluid should be changed frequently, even though it 



