120 CYTOLOGICAL TECHNIQUE 



Dye solutions are usually made with haematoxylin instead of 

 haematein. It will be remembered that the former, if pure, is 

 colourless (p. 94). It has the advantage of being more soluble 

 than haematein in water and in aqueous alcohoHc solutions. 

 Gradual oxidation by atmospheric oxygen keeps up the strength 

 of solutions for a long time. It is convenient to oxidize about 

 a quarter or a half of the haematoxylin by sodium iodate when 

 making up a solution, and to allow the rest to remain as a re- 

 serve. ^^ Solutions made in this way are ready for immediate use 

 and last a long time. The reserve is gradually oxidized. 



Two of the most useful solutions containing aluminium haema- 

 tein are Delafield's and Ehrlich's. They are called haematoxylin 

 solutions, because it was intended by their inventors that they 

 should be made up with the unoxidized substance, reliance being 

 placed on atmospheric oxygen for gradual production of the dye. 



In Delafield's haematoxyhn^^- the mordant is ammonium alum. 

 Glycerol and methanol act as solvents, disinfectants, and re- 

 strainers. The stock solution may be diluted as desired with dis- 

 tilled water. It is necessary to put the tissue in alkaline tap-water 

 or weak ammonia solution after soaking it in the mordant/dye 

 solution, for the alum is rather strongly acid and this prevents 

 lake-formation. The tissue changes in colour from dirty red to 

 clear blue, and the basiphil objects are then clearly revealed. This 

 is an excellent dye when used progressively by experienced 

 workers, but it is perhaps rather too quick in action for the be- 

 ginner. It is suitable for whole mounts as well as sections. 



In Ehrlich's haematoxylin^^ the mordant is potassium alum. 

 Glycerol is contained in this solution, as in Delafield's, but 

 ethanol takes the place of methanol. The chief diff"erence from 

 Delafield's is that acetic acid is added to prevent the formation of 

 an insoluble lake. As a result the solution keeps almost indefin- 

 itely, and this is its great virtue. Dyeing takes much longer than 

 with Delafield's. Ehrlich himself worked progressively, but it is 

 usual to over-dye and extract the excess with weak aqueous 

 hydrochloric acid. 'Blueing' by an alkaline solution is necessary. 



Ferric iron is a valuable mordant for haematein. Simple ferric 

 salts work well, but iron alum, Feo(S04)3.(NH4)2S04.24H20, is 



