THE BLOOD DYES 273 



fluenced the final result of the dyeing of the protozoan nucleus by 

 Giemsa's method, even though eosin by itself does not colour 

 it.) 



Br Br ^ 



Br Na+ -O.^WY 



^^ A ^^ \/ 



Potassium / \C\ Resorcinol 



trior omopnenolate L J ^O" Na+ 



Eosin Y 



Partly as a result of his researches on the nuclei of free-living 

 amoebae, ^^^ Unna came to the conclusion that the substance in 

 the nuclei of Protozoa that reacts with Romanowsky dyes to give a 

 red colour is not acidic chromatin, but the highly basic protein, 

 protamine. He considered that eosin (or a substitute) combined 

 chemically with this and also with the basic dye. The latter he 

 believed to be the imino-base of asymmetrical dimethylthionine 

 (azure A). The imino-bases of the azures are red. If one of these 

 is in fact responsible for the colouring of the protozoan nucleus, no 

 question of metachromasy arises. The evidence suggests strongly 

 that the desired colour is best given when azure B and eosin (or a 

 substitute) are present; but whether the azure acts as a base or 

 metachromatically as an ion, whether the substance dyed is really 

 protamine, and how the eosin affects the result, are still unsolved 

 problems. 



A full explanation of Romanowsky dyeing has not yet been pro- 

 vided, but the main outline of the process is understood and 

 sufficient knowledge has been gained to allow the preparation from 

 pure dyes of solutions that can be relied upon to give the striking 

 effect that is desired. 



