430 PRACTICAL DIRECTIONS. [APP. 



matoxylin, and should be removed directly from 

 absolute into the haematoxylin. 



The time required for staining varies with 

 the size of the object and the strength of the 

 staining fluid. Hsematoxylin will not stain if 

 the embryo is not quite free from acid. 



If the embryo is stained too dark, it should 

 be treated with a solution of 70 p.c. alcohol 

 acidulated with nitric acid (*25 p.c. of acid) 

 until the excess of staining is removed; and in 

 all cases the hsematoxylin staining is improved 

 by treating the embryo with acidulated 70 p.c. 

 alcohol. 



After staining the embryo must be well 

 washed in 70 and placed in 90 p.c. spirit. 



b. With borax-carmine. 



Make an aqueous solution of 2 to 3 p.c. 

 carmine and 4 p.c. borax, by heating: add an 

 equal volume of 70 p.c. alcohol, and let the 

 mixture stand for thirty-six hours; after which 

 carefully filter. 



Stain the object thoroughly by leaving it in 

 this solution for one or even two days; it will 

 attain a dull maroon colour : transfer it then to 

 acidulated alcohol (see a) until it becomes a 

 bright red, and afterwards keep it as before in 

 90 p.c. alcohol. 



This staining solution permeates more tho- 

 roughly and uniformly a large object than does 

 hsematoxylin : therefore when a four or five day 

 chick is to be stained, borax-carmine is the best 

 staining reagent to use. Embryos that have 

 been preserved in corrosive sublimate will be 



