56 CHAPTER V. 



tates corrosive sublimate instead of dissolving it. That is true, but the 

 precipitate is soluble in excess of the precipitant. 



It is important that the sublimate be thoroughly removed 

 from the tissues, otherwise they become brittle, and will not 

 stain so well. They will also become brittle if they are kept 

 long in alcohol. 



It may happen that if the extraction of the excess of subli- 

 mate from the tissues in bulk has been insufficient, crystals 

 (of some mercurial compound) may form in the sections after 

 they have been mounted in balsam. This may easily be pre- 

 vented by treating the sections themselves with tincture of 

 iodine for a quarter of an hour before mounting. This will 

 do away with the necessity of treating the tissues in bulk 

 with iodine, which is frequently a very long process (unless 

 it is desired to keep the material for a long time in alcohol 

 before making the sections). 



MANN (Zeit. f. wiss. Mik., xi, 1894, p. 479) prefers treat- 

 ing the sections rather than the tissues in bulk, on the 

 ground that the iodine makes them soft, so that they shrink 

 on coming into paraffin. SCHAPEE (Anat. Anz., xiii, 1897, 

 p. 463), on the other hand, has shown that neglect to extract 

 the sublimate from the tissues in bulk may give birth to 

 serious artefacts, which appear to arise during the imbedding 

 process. 



You may stain in any way you like. Carmine stains are 

 peculiarly brilliant after sublimate. 



It must be remembered that the solutions must not- be 

 touched with iron or steel, as these produce precipitates that 

 may hurt the preparations. To manipulate the objects, wood, 

 glass or platinum may be used ; for dissecting them, hedge- 

 hog spines, or quill pens, or cactus spines. 



When properly employed, sublimate is for general work 

 undoubtedly a most useful fixing agent. It is applicable to 

 most classes of objects. It is perhaps less applicable, in the 

 pure form, to Arthropods, as it possesses no great power of 

 penetrating chitin. For cytQlogical work it is, according to 

 my experience, not to be trusted, and only to be recommended 

 where more precise fixing agents, such as solution of Flem- 

 ming, are counter-indicated by reason of their lack of pene- 

 tration, or the like. Amongst other defects it has that of 

 frequently causing serious shrinkage of cells. 



