Untersuchungsmethoden. 



155 



It has long been known to those who have used a watery solu- 

 tion of extract of haematoxylin and alum (one part of the extract to 

 three of alum, as recommended by Professor Arnold and Dr. Klein) 

 that in certain cases the resulting fluid is purple, at other times 

 blue, and occasionally red. The red solution gives a disagreable co- 

 lour to the sections, and also stains very slowly. 



In working with various microscopical specimens of the thymus, 

 it was found, however, that certain tissues were well stained by the 

 red solutions, and others readily by the blue. It has been my custom 

 in many cases to double stain the specimens, using first a red solu- 

 tion, and deepening the staining of the specimen, and making parts 

 of it purple-blue. 



The method adopted is to leave them in a rather strong (red) 

 solution from sixteen to eighteen hours. They are then washed and 

 placed in a weak blue solution, from four to twenty-four hours. It is 

 necessary to use the red fluid of such a strength that it will not 

 change to blue, even during three or four days' exposure; and to in- 

 sure this it is better to use it rather strong, as all weak solutions 

 are more liable to turn blue. It is also better to keep the red so- 

 lution very strong, and to filter a few drops of it into a watch-glass 

 of water to the required strength each time it is used, as all filtering 

 tends to turn the solution blue, especially if a clean dry filter -paper 

 is used; and the filtering of weak solutions is prejudicial to the red 

 colour. The blue solution is used with more water, because the 

 weaker the colour the bluer the specimen. 



Specimens of thymus treated in this way will, in most cases, 

 show double staining; the difference of colour, it is true, is not much 

 marked, but still is quite sufficient to clearly distinguish the cortical 

 from the medullary part of the follicle, or to stain the granular cells 

 of the thymus, and the surrounding protoplasm, of two distinct colours. 



The red haematoxylin stains the connective -tissue, and the pro- 

 toplasm of the connective -tissue -corpuscles and of the granular cells, 

 and the walls of the vessels; while the blue deeply stains mucus, al- 

 most all nuclei, the reticulum, and the lymphoid corpuscles. 



As a rule, if only a single staining is used, the solutions which 

 are of a purple colour are much the best; the red haematoxylin so- 



