17. ROSANILIN HYDROCHLORIDE.

This stain is useful for double and treble staining; for this purpose a strong solution must be made in rectified spirit. Place some of the crystals in a glass mortar and rub up with a little spirit, add more spirit, until all the crystals are dissolved. This will do for the ordinary staining processes. It is also used in a special manner for the Tubercle Bacillus, and the method of making the stain will be given under that head.

18. ROSANILIN ACETATE.

It

This is a useful stain for blood corpuscles. must be rubbed up in a mortar with rectified spirit, and when thoroughly dissolved an equal quantity of distilled water added—5 grammes of the crystals to 100 c.c. of spirit and thoroughly dissolved; then 100 c.c. of distilled water added-this makes a good strength for general use.

19. SAFRANINE.

This colour is useful for the detection of amyloid degeneration. A one per cent. solution is Imade with distilled water and filtered. The sections must be left in the stain for half an hour and then washed well in water. They must then be

placed in methylated spirit and washed until the colour comes away very slowly. A little practice is required to do this properly, as if they are left too long all the colour will come out, and if they are not washed enough in the spirit they have an opaque blurred appearance.

20. CHRYSOIDIN.

This stain is of no use for tissues, but is very useful as a contrast stain for micro-organisms.

It is very transparent, and where the structure of minute organisms is to be studied under high powers, it is a great assistance to the violet or blue with which they are stained.

A two per cent. solution in distilled water is the best strength to use.

21. BISMARCK BROWN, VESUVIN.

These by some are considered to be the same stains. But this is not the case, as the Bismarck Brown sold in this country is only slightly soluble in water, and is not a satisfactory stain to use. Vesuvin on the other hand is freely soluble.

There are, however, several kinds of Vesuvin, and some are of no use in staining tissues.

There are two kinds which stain well, but with somewhat different results, and it is necessary to try

them both in special cases to find out which is most suitable. They can be obtained from Messrs. R. & J. Beck.

In either case a 5 per cent. solution is made in distilled water, and if this is too strong and stains too quickly it must be diluted.

These stains are very pleasant to the eye, and differentiate very well if properly used.

This is also a good stain for injected tissues, such as liver when the ultimate bile-ducts have to be examined. Its action as a double stain with indigocarmine will be mentioned further on.

22. SPILLER'S PURPLE.

This is a very useful colour for tissues both for double and single staining.

The solution must be strong and the sections must be left in for some time as a good deal of the colour washes out in spirit.

To make the stain :

Rub up 2 grammes of the colour with 10 c.c. of alcohol in a glass mortar, then add 90 c.c. of distilled water, making a 2 per cent. solution.

This may be diluted in some cases. It is necessary to get Spiller's Purple No. 1 for the best results.

The formula for use with bacteria will be given under that head.

Gold Chloride, Silver Nitrate, Osmic Acid. These

E

selective stains, having a hardening as well as staining action, have been considered under the head of hardening agents. See pp. 19-23.

* Solutions of all these stains can be obtained ready for use from Messrs. R. & J. Beck, 68 Cornhill.

CHAPTER V.

DOUBLE STAINING.

By double staining is meant a process in which two colours are taken, which have affinities for different elements in the tissues to which they are applied. Thus while one colour will stain the connective tissue and protoplasm of cells, the other will colour all nuclei and so differentiate the different elements as to

make them more easily discernible. Others again will stain different glands according to their secretions. Thus showing a distinct chemical reaction between glands differing in their functions.

In other cases the duct of a gland can be stained of a different colour to the surrounding tissue and its own secreting substance, by which means it is easy to distinguish it, and thus show if it is implicated in any morbid change, and also in some cases prove whether the morbid change is primary in it, or has extended. from surrounding tissues, in which case all the ducts. would not probably be similarly affected.

Double staining is a subject that requires to be very much more worked out than it has been hitherto, and in the present work, those processes only will be given in detail, which have been fairly well tried; many other combinations of staining agents will be apparent to the student, which have not yet been worked out,