STAINING. 41 



section floating in the alcohol. The sections adhere to the paper, and in 

 this way the entire surface of the strip may be covered by series of sections. 

 To prevent the drying of the sections, a number of such strips are laid 

 in rows on a layer of blotting-paper moistened with 70% alcohol. A glass 

 plate of corresponding size is painted with very fluid celloidin. After the 

 layer of celloidin is dry, the strips of paper are laid, one by one, on the 

 glass plate, with sections downward, and the fingers gently passed over 

 the reverse side. This process is continued until the entire surface of 

 the glass is covered. On carefully raising the strips it is seen that the 

 sections will adhere to the layer of celloidin. (To prevent drying, 

 sections must- be kept moistened with 70% alcohol.) After first drying 

 the sections with blotting-paper, a second layer of very thin celloidin is 

 painted on the surface of the glass plate. When this layer is also dry, 

 the plate with its adherent sections is placed in water. Here the double 

 layer of celloidin containing the sections is separated from the glass, and 

 is ready for further manipulation. Before mounting, the sheet of celloidin 

 is cut with scissors into convenient portions. 



In the case of celloidin sections, if it be desirable to preserve 

 the surrounding celloidin, care should be taken that the preparations 

 should not come in contact with any agents dissolving celloidin. These 

 latter are alcohols from 95% upward, ether, several ethereal oils, especially 

 oil of cloves, but not the oils of origanum, cedar wood, lavender, etc. 



2. STAINING. 



It is in most cases necessary to stain tissues to bring clearly to view 

 the tissue elements and their relation to each other. The purpose of 

 staining is therefore to differentiate the tissue elements. The differential 

 staining is due to the fact that certain parts of the tissue take up more stain 

 than others. Staining of sections may be looked upon as a microchemic 

 color reaction, and has therefore a value beyond the mere coloring of 

 sections so that they may be seen more clearly. 



Broadly speaking, stains used in microscopic work may be divided 

 into basic stains, which show special affinity for the nuclei of cells and are 

 therefore known as nuclear stains, and acid stains, which color more 

 readily the protoplasm protoplasmic stains. Certain stains, which we 

 may know as selective stains (they may be either basic or acid), color one 

 tissue element more vividly than others, or to the exclusion of others. 

 Since the various tissue elements show affinity for different stains, prepa- 

 rations may be colored with more than one stain. Accordingly we have 

 simple, double, triple, and multiple staining. 



Certain stains are also especially adapted for staining in bulk or mass 

 that is, staining a piece of tissue before it is sectioned. 



SECTION STAINING. 



Carmin. Aqueous Borax=carmin Solution. 8 gm. of borax 

 and 2 gm. of carmin are ground together and added to 150 c.c. 

 of water. After twenty-four hours the fluid is poured off and filtered. 

 The sections, previously freed from paraffin and treated with alcohol, are 

 placed in this fluid for several hours (as long as twelve), and then washed 

 out in a solution of 0.5 to \<'/ f hydrochloric acid in 70^ alcohol. 

 They are then transferred to jo f / f alcohol. 



Alcoholic Borax-carmin Solution. 3 gm. of carmin and 



