xlvi INTRODUCTION. 



(c) Osmic Acid. Make a one per cent, solution which can be diluted as required to \ or \ 

 per cent. The method of using and preserving this substance has already been referred to 

 under Hardening Solutions (p. xxxii). It is useful for blackening fat-cells, and for fixing the 

 white substance of Schwann in nerve-fibres, though it has many other important applications. 



ON DOUBLE-STAINING OF TISSUES. 



By using two differently coloured solutions, it is found that in certain tissues one part 

 will take up one colour, whilst another part takes up another. Some glands stain of a green 

 colour with iodine-green e.g. the mucous glands of the tongue whilst the other glands, the 

 serous glands, are not affected by it. 



This method is of the greatest value, and I find it can be practised very successfully by 

 students even in large classes. 



PICROCARMINE. 



As already indicated, this dye stains certain parts yellow and other parts red, hence its 

 value. 



PICROCARMINE AND LOGWOOD. 



Stain the sections slightly with picrocarmine, and after washing them in water, place 

 them in dilute logwood solution, in which they must not remain too long. They soon be- 

 come lilac-coloured. Wash them and mount them. This method is useful for the mesentery 

 of the newt (p. 38), for developing bone, epiglottis, &c. 



PICROCARMIME AND IODINE GREEN. 



This is one of the most useful combinations I know. Stain the sections in picrocarmine, 

 and wash them well in water slightly acidulated with acetic acid, and then stain them in a 

 watery solution of iodine-green (p. xlv), taking care that they do not become over-stained, 

 which can easily be ascertained by washing them in water. If a section of the posterior third of 

 the tongue be so stained (p. 61), all the muscles and connective tissue are red, whilst the mucous 

 glands and adenoid tissue are green. The serous glands do not take up the green stain. This 

 combination is, therefore, of the utmost value for gland-tissue. All the mucous glands and 

 adenoid tissue of the intestinal tract become green, whilst the connective tissue is red, and the 

 non-striped muscle of a light yellow or brown. Most exquisite effects are produced in the 

 cerebellum, bone, and intestine by this method. The sections must be mounted in dammar. 



EOSIN AND LOGWOOD. 



Stain the sections lightly in eosin and then in logwood. This does very well for the 

 brain. 



GOLD CHLORIDE AND SILVER NITRATE. 



This method is sometimes employed for the cornea, which is first impregnated in the usual 

 way with gold chloride and then with silver nitrate. The method is very difficult to be suc- 

 cessful with and often fails. 



