134 Proceedings. 



the differentiation of structures and tissues, which junior 

 students have a difficulty in distinguishing in unstained 

 sections, and which more advanced students want to see 

 clearly and readily without hesitation or loss of valuable 

 time. For this object, the method of double staining, which 

 I am about to describe, appears to me to be one of the most 

 useful. I may go further, and say that of the many methods 

 I have used during the last twelve or fifteen years, this 

 one has been found the most generally applicable, the most 

 reliable in its results, and the most permanent. There are 

 other advantages, in addition to these, but they will be best 

 considered when the method has been described. The 

 colours used are a blue and a red, the one being the well 

 known aniline blue, and the other, known in some dye works 

 as cotton red, is, I believe, a form or derivative of carthamine. 

 Both are used in aqueous solution. To the blue solution a 

 definite quantity of saturated solution of picric acid is added, 

 so that it may be termed the picric and blue solution. The 

 composition of the solutions is usually made up as follows, 

 though slight deviations are not material, and in some cases 

 may be desirable : — 



Picric and Blue Solution : 



Aniline Blue o" i gram. 



Water 35 c.c. 



Saturated Solution of Picric Acid 15 c.c. 



Cotton Red or Carthamine Solution : 



Cotton Red or Carthamine o* 1 gram. 



Water 25 c.c. 



The Picric and Blue solution is ready for use as soon as 

 made, and so is that of the Cotton Red. But sometimes the 

 latter is not quite clear, owing to the presence in the dye of 

 some insoluble material. In that case it may be filtered, 

 though this is not really necessary, as the presence of the 

 insoluble substance does not interfere with the action of 

 the dye and is removed from the sections in the subsequent 



