AND HOW TO USE IT. 107 



has been made to act). To prevent this, it is important that the 

 glycerine used to preserve the preparations should be slightly 

 tinged with picric acid, and if balsam is used, it is necessary to 

 dehydrate the preparations in alcohol, containing also a small 

 quantity of picric acid in solution. In the latter case, after this 

 treatment, the preparations may be at once placed in oil of cloves 

 or turpentine without fear of the stain suffering from it. If it is 

 intended from the first to mount the preparations in balsam, the 

 operation may be abridged by transferring the specimen immedi- 

 ately from the solution of anilin blue to a bath of alcohol to 

 dehydrate it, the alcohol containing J per cent, of picric acid in 

 solution. Intestinal injections may also be made with it, and small 

 artificial oedemata may be produced with a Praraz's syringe. In the 

 lymphatic gland the colouring matter can be made to penetrate 

 into the cavernous system, where the endothelial cellules may be 

 recognised lightly coloured green. If a small oedema be produced 

 under the skin of the groin in a rabbit or guinea-pig, the connec- 

 tive cellules and fibres between which they are situated may be 

 studied to perfection by means of eosin, which is soluble in water 

 (Renant). The picric anilin solution may be well employed in 

 interstitial injections, when the picric acid, instead of being dis- 

 solved in water, is dissolved in one-third part of alcohol. Prepa- 

 rations thus stained are not affected by the weak acids — acetic, 

 phenic, etc. — whilst alkaline solutions rapidly destroy their 

 beautiful outline. The picric acid solution is especially recom- 

 mended for the study of the lymphatic glandular system, 

 complete sections of the medulla oblongata, and normal and 

 pathological tissues. 



Double Staining with Eosin and various colours (Schieffer- 

 deckar). — The advantage of this method is that it can be applied to 

 preparations hardened either in alcohol or chromic acid. The 

 eosin is used according to Fischer in an alcoholic solution, one 

 per cent, solutions in water are made of dahlia, methyl-violet, and 

 anilin green (alcoholic solutions do not stain enough to be of use, 

 eosin cannot be mixed with the other colours). Stain the section 

 in a small dish containing alcohol, to which a few drops of eosin 

 have been added. Time varies from half an hour to several 

 hours; being left too long in the eosin is not detrimental. The 



