408 E. HANBURY HANKIN. 



is that the bacteria^ if at all easy to stain, are dyed black, which 

 result, for obvious reasons, should generally be avoided. 



In all these methods of staining, advantage is taken of the 

 well-known fact that benzine does not dissolve, and therefore 

 fixes the aniline dyes. Sections when stained so feebly that 

 prolonged washing in alcohol would render them quite colour- 

 less, are placed in benzine after dehydration, and the loss of 

 colour being thus checked, they are mounted as permanent 

 sections. If, however, they were removed directly from the 

 alcohol to the benzine, a precipitate of dye would probably be 

 formed on the surface of the section, which would spoil the 

 result. Hence the necessity for the benzine and oil of cloves 

 mixture, which, refusing on the one hand to dissolve much 

 more of the dye, and on the other to precipitate any, forms a 

 link between the alcohol and the benzine. Sections should 

 generally be placed successively in two or three watch-glasses 

 or capsules full of this mixture before removal to benzine ; and 

 in the last of the series they should only remain while they are 

 being spread out on a lifter. By taking this precaution the 

 last capsule will contain little dissolved dye, and all granular 

 precipitate on the section is prevented. 



Another advantage in placing sections in benzine before 

 mounting is that any residue of clove oil is removed. By this 

 means the section is far more likely to be permanent than if 

 the excess of clove oil is merely drained off with a piece of 

 blotting paper, as is usually the case. 



In using these methods it is necessary to remember that 

 fuchsin and other dyes which show such an affinity for nuclei 

 when dissolved in water or alcohol, act quite differently when 

 dissolved in oil of cloves. Under these conditions they are 

 almost incapable of staining bacteria or nuclei, but the whole 

 of the tissue becomes dyed of a uniform tint. This influence 

 of the solvent in modifying the action of the dye is not of a 

 chemical but rather of a physical nature, for the oil of cloves 

 may be replaced by aniline, creosote, or any clearing agent, with 

 scarcely any alteration in the result. 



If a section is placed in water and some alcoholic fuchsin 



