THE BLOOD DYES 265 



Meanwhile Romanowsky ^^^ went on to study the multiphcation 

 of the nucleus and the life-history of the parasites, and clinicians 

 soon made use of his method as an invaluable aid to diagnosis. 



The complications behind Romanowsky's dye can best be 

 elucidated by the historical method. The accompanying evolution- 

 ary diagram will help to explain the course of progress. The reader 

 may care to turn back to this diagram from time to time while 

 following the development of the storv'. It leads from Romanow- 

 sky's brilliant but empirical and not always repeatable results to 



Romanowsky 

 (1891) 



Unna 

 (1891)' 



Jenner 

 (1899) 



Xocht 

 (1898) 



Reuter 

 (1901) 



Leishman 

 (1901) 



Giemsa 



(1902a, b, 1904, 

 1907, 1924) 



IVIacNeal 

 (1906, 1925) 



Roe, 

 Lillie, 



& 



Wilcox, 



(1940) 



The evolution of blood dyes 



the sure and scientific preparations of Giemsa, Roe and his col- 

 leagues, and AlacNeal. Care has been taken to exclude from this 

 account all those methods — some of them very well known — that 

 did not lead towards the goal of understanding. Bernthsen ^^ and 

 Kehrmann,-^^ who played particularly important parts, have been 

 omitted from the diagram because their influence on the course of 

 research cannot be indicated without making it too complicated. 

 A Londoner, Jenner,^^^ discovered that the precipitate formed 

 on mixing solutions of eosin and methylene blue was particularly 

 soluble in methanol. Subsequent workers have mostly made use 

 of this fact instead of relying on the solubility of the neutral com- 

 pound in excess of the acid or basic dye (though some excess of 

 the basic has usually been allowed). Jenner, however, did not 

 obtain the wide variety of colours seen in a successful Romanowsky 

 preparation. Similar results were obtained in Germany by May 

 and Griinwald,^-^ who sometimes used a fresh mixture of eosin and 

 methylene blue before it had time to precipitate, sometimes 

 allowed precipitation to occur and then dissolved it in methanol. 

 Preparations made by these methods are useful enough for certain 

 purposes. The red blood-corpuscles are bright red, eosinophil 

 granules deep red, the nuclei of leucocytes and the basiphil cyto- 

 plasm of lymphocytes and of the malarial parasite blue. The blue 



