PRACTICAL MICROSCOPY. 



purple too light; so you may return it to the haema. for another 

 period of two or three minutes, which will probably give sufficient 

 depth. 



As the section floats on the washing water, you will notice that the 

 latter will be colored by the dye, some of which leaves the tissue. 

 Allow the water to act until no more color comes out. The tint of 

 the section changes from purple to violet, and the water must be al- 

 lowed to act until the change is complete. Again, you will remem- 

 ber that this dye contains alum and, if you hurry the washing, you 

 will undoubtedly find crystals covering your specimen after it has 

 been mounted. From five to ten minutes will complete the washing. 



If you were to examine your section at this stage, you would find it 

 opaque, and, as we are obliged to study our objects mainly by trans- 

 mitted light, we must find some means of securing translucency. 

 The essential oils are used for this purpose, oil of cloves being com- 

 monly employed. Lift the section from the water with the needle; 

 let it drain a moment, and then drop it into the alcohol with which 

 the salt-cellar was filled. The object of this bath is the removal of 

 the water from the tissue, and this will be accomplished in from five 

 to ten minutes. Again lift the section, and place it in the oil of 

 cloves. The tissue floats out flat, and in a few minutes sinks in 

 the oil. 



We might proceed to the examination of the stained section; but I 

 shall ask you to let it remain in the oil, covering the box carefully to 

 exclude our great enemy, the dust, until we have learned more about 

 staining. 



FIG. 14. DIAGRAM INDICATING THE SUCCESSIVE STEPS IN STAINING WITH THE H.EMATOXYLIN 



SOLUTION. 



To recapitulate: The essential steps in the haema. process are: 



1. Staining the tissue haema. 



2. Washing water. 



3. Dehydrating alcohol. 



4. Rendering translucent oil of cloves. 



