VII 

 METHODS OF STAINING 



The staining of eggs may be discussed from two points of 

 view; staining of the living egg and staining of the fixed. 



Intra-Vitam Staining 

 Living cells are often stained with dyes which do not impair 

 their viability. Among such stains are methylene blue, neutral 

 red, janus green, nile blue sulfate, etc. The precaution to be 

 taken in using such vital dyes )s to avoid concentrations that 

 are toxic. The stains are therefore made up in sea-water in 

 such way as to give the barest perceptible tinge of color. 

 Wherever possible dyes employed should be of the same manu- 

 facture. Even so, the proper concentration has to be worked 

 out for each case, because these dyes vary greatly. The stained 

 eggs should be as perfectly viable as the normal unstained. No 

 set rule can be given as to the exact dilution of dye. One should 

 make up a series of dilutions, taking the most dilute that stains 

 the cell. If this be toxic, as shown by failure or any abnormahty 

 of development, this particular make of dye should not be used; 

 another should be tried. 



Staining of Fixed Eggs 



Fixed eggs may be stained in toto or alter havmg been 

 sectioned. 



In toto staining 

 In toto staining is often very useful. It may be the sole 

 method for the study of the fixed egg or may be employed as an 

 aid for the study of stained sections. In the former case the 

 eggs are best fixed in solutions which do not contain osmic acid, 

 since this blackens the egg to such an extent that details of 

 structure are not easily visible. One should rather use fixatives 



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