THE STAINING OF COVER-GLASS PREPARATIONS. 99 



absorbed. Some, indeed, are nearly colourless. If 

 they are left for a longer time in the weak alcohol, 

 some are sure to lose all their colour, whilst others 

 will retain it more or less, and this difference remains 

 approximately true, even if they are left for hours in 

 the fluid. It is true that little by little minute quan- 

 tities of stain are extracted from the preparations, so 

 that soaking for days in the weak alcohol makes them 

 colourless. A stronger effect is produced by a more 

 concentrated solution of alcohol, and still stronger 

 ones by solutions of acids, as we shall see later on. 



