42 THE MICROSCOPE AND HOW TO USE IT. 



or two ; bear in mind that this colour cannot be washed out again 

 if too deep. Although the spirituous stain may do, it is better to 

 have a section apparently overstavied in the rosanilin solution, 

 while it is even under-stained in the iodine green. After washing, 

 mount the sections in the usual way. (A good deal of the 

 rosanilin will come out in the second immersion in spirit, which 

 it is necessary to change until no more colour comes away ; 

 otherwise the oil of cloves and Canada balsam will be coloured, 

 and the specimen spoilt). The results vary with the length of 

 time the section is immersed in each of the two last colours, and 

 also the strength of the solutions. If the sections are to be laid 

 aside before mounting they should be kept in oil of cloves. The 

 best results are obtained from material soaked in chromic acid, 

 when only a few are stained at once. The staining process is 

 well shown in a section of the base of a cat's or dog's tongue, cut 

 through one of the circumvallate papillae, including some of the 

 mucous glands. Muscle fibres, connective tissue, protoplasm of 

 cells, etc., stained with picro-carmine, are red ; all nuclei in the 

 superficial epithelium, serous glands, non-striped muscle tissue, 

 in vessels, etc., are green. Take only a few sections at a time 

 and do not hurry over the different processes, after a few trials the 

 exact time of immersion will be learnt, and should be recorded. 

 Always keep a note-book handy, and enter any little items which 

 are likely to prove useful in future work. 



Staining with four, five, and six different pigments, (i) Picro- 

 carmine or eosin, (2) logwood, (3) aniline rose, (4) aniHne green, 

 and (5) iodine. If the tissue has been already stained in gold 

 chloride or nitrate of silver, which also gives good results, six 

 stains will have been used. I have seen specimens so stained, 

 such as sections of Tongue with taste organs, salivary gland, 

 ovary, and testis ; in each case the different parts came out with 

 remarkable distinctness. 



11.— Gold Chloride and Anilines.— Striking results may be 

 obtained by first staining fresh tissues, especially growing bone, in 

 a chloride of gold solution, then decalcify and harden in spirit. 

 When hardened sufficiently, sections may be cut and stained with 

 two colours. What action chloride of gold has on those parts, 



