106 THE MICROSCOPE 



Process of Colouring Preparations with Picric Acid and 

 Aniline Blue Solution.* — This is very useful, both for normal and 

 pathological specimens. It is well known that certain tissues — as 

 spleen, lymphatics, cerebral, and spinal nervous tissues — retain 

 their colour better and with more elegance when anilin blue is 

 used- Picric acid and anilin blue, mixed together either by sub- 

 jecting the preparations to be stained to a solution of aniline, and 

 then to another of picric acid. The solutions, whether of picric 

 acid or anilin, ought to be saturated, which can be done easily by 

 leaving an excess of each substance at the bottom of the vessels 

 in which the materials are placed to dissolve. In this way we are 

 always sure of using only saturated solutions. When it is re- 

 quired to make use of the picric anilin solution, loo cc. (for 

 example) should be taken of the saturated watery solution of 

 picric acid, and into it should be poured 4 or 5 cc. of the blue 

 liquid, also saturated. The resulting solution stains admirably a 

 preparation of the lymphatic glandular system in the space of a 

 few minutes. If it is desired to use the two substances separately, 

 keep the preparation in the anilin solution for a few minutes, and 

 afterwards place it in picric acid. In working thus, we can see 

 that the preparation is not stained too much by the analin, and to 

 this end it is well to take it out so soon as it has acquired a light 

 sky-blue tint. By taking it out now, one is always sure that it will 

 show the nuclear elements sufficiently coloured, whilst the proto- 

 plasmic parts and others will be only very slightly stained. By 

 waiting until the preparation has taken a dark-blue tint, and then 

 submitting it to picric acid, it becomes obscure and confused. 

 Preparations treated with the anilin solution, as above, and placed 

 in picric acid, pass in the course of 15 minutes from sky-blue to a 

 delicate green. The tissues show the nuclei, both free and cellu- 

 lar, stained green ; the protoplasm and the fibres coloured pea- 

 green, though faintly and with a delicate tint. It is possible to 

 stain with great advantage not only fresh tissues, but also those 

 which have been subjected to different hardening re-agents, such 

 as alcohol, chromic acid, bichromate of potash, etc. Preparations 

 obtained by these processes may be preserved like others in fluids 

 or balsam (note, that picric acid, being soluble in water and alco- 

 hol, might easily be removed from the preparations upon which it 



* Journal de Micrographics 



