GENERAL METHODS. 21 



erers closely resemble methods long known, yet a thorough 

 trial of all possible salts, acids, and coloring matters should 

 not be omitted. In consequence of the slight insight which 

 we have been able to obtain into the mechanics of staining,, 

 it is only possible to discover useful methods in a purely 

 empirical way ; and we cannot yet conceive how far newly- 

 discovered stains or new methods may lead toward further 

 conclusions concerning the structure of the protoplasmic 

 constituents of the cell. 



31. The result of staining is dependent not only on the 

 nature of the stain used and of its solvent, but also largely 

 on the previous treatment of the object, especially on the 

 fixing medium. Besides, useful results may be obtained 

 after staining by treatment with various solutions of salts,, 

 acids, alkalies, and the like, or by the combination of differ- 

 ent stains. 



We shall become acquainted in the third part of this book 

 with a large number of methods for fixing and staining, 

 But here only the general technique of fixing and staining: 

 will be described. 



A. FIXING. 



32. Fixing is generally the more complete the more 

 rapidly the fixing fluid reaches the cells to be fixed ; there- 

 fore the best results are obtained with solutions as concen- 

 trated as possible, so far as they do not cause precipitates or 

 exert any destructive action. Further, small objects are 

 more quickly penetrated by fixing fluids than larger ones,, 

 and therefore in difficult cases the smallest possible pieces,, 

 even to sections a few cells in thickness, should be pl'aced 

 in the fixing fluid- 

 It should be especially observed that cuticle and cork are 



not easily permeable by most fixing fluids and indeed are 

 quite impermeable by some. One may, therefore, often 

 greatly aid the penetration of fixing fluids by removing: 

 suberized membranes as far as possible, or at least by splitting: 

 them to furnish points of entrance for the fluids. 



From the above it follows that, in objects which have not 



