38 STUDENTS HISTOLOGY 



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 allowed to act until the change is complete. 



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 transmitted light, we must find some means of securing trans- 

 lucency. The essential oils are used for this purpose, oil of cloves 

 being commonly 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 saltcellar 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 we shall ask you to let it remain in the oil, covering the box 

 carefully to exclude our great enemy, dust, until we have learned 

 more about staining. 



To recapitulate: The essential steps in the haematoxylin pro- 

 cess are: 



1. Staining the tissue haematoxylin. 



2. Washing water. 



3. Dehydrating alcohol. 



4. Rendering transparent oil of cloves. 



As the section is put in the dye, care should be taken to so float 

 it out that it may not be curled. This is easily done with the 

 needle. After the alcohol bath, however, this becomes difficult, as 

 the tissue is rendered stiff by the removal of the water. 



This is the simplest and best of all methods for general work, 

 and you are advised to master every detail of the process. After 

 reading the directions which we have given, and having never seen 

 the work actually done, it will not be singular if you conclude 

 that the staining of tissues is a tedious and slow process; but after 

 a month's work you will be able to stain fifty different sections in 

 half an hour, and have them ready for mounting. 



HJEMATOXYLIN AND EOSIN DOUBLE STAINING 



Very beautiful and valuable results in differentiation are 

 obtained by staining first with haematoxylin and subsequently with 

 eosin. Eosin, a coal-tar derivative, stains most animal tissues 



