CHAPTER 10 



The Direct Attachment of Dyes 



to Tissues 



An insoluble pigment requires the addition of an adhesive if it 

 is to remain in position when applied to any object. A dye is pre- 

 sented in solution without the addition of any adhesive ; it is not 

 itself sticky or obviously adhesive; yet it adheres. It is the purpose 

 of this chapter to explain the reason for this. 



It has already been mentioned (p. 172) that certain dyes are 

 used with intermediaries between themselves and the tissues. 

 These intermediaries or mordants are not adhesive in any 

 ordinary sense. Chapter 11 (p. 207) deals with the use of these 

 substances. 



The nature of the process of dyeing has been studied more 

 elaborately by the research-workers of the textile industry than by 

 those who use dyes in microtechnique. This is due partly to the 

 fact that larger funds are available in industry and partly to the 

 relative homogeneity of the textile fibres — especially cotton — in 

 comparison with the kinds of tissues usually studied by biologists. 

 It must be confessed also that the practical dyer has generally 

 adopted a more scientific approach to his work than the histologist 

 and cytologist. As Mann ^^^ unkindly remarked: — 



'The method of staining, once having taken root in the animal 

 histologist, grew and grew, till to be an histologist became 

 practically synonymous with being a dyer, with this difference, 

 that the professional dyer knew what he was about, while the 

 histologist with few exceptions did not know, nor does he to the 

 present day.' 



The realization of this truth is helpful to the biologist, but it is 

 necessary to point out another truth that has been overlooked, 

 namely, that there are many very important differences between 

 the dyeing of textile fibres and the dyeing of tissues in biological 



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