STAIN[Nfi. iO-i 



the prolonged washing necessary for most sections, and to 

 suppress altogether the dehydration by alcohol, his cover- 

 glass preparations being simply dried after staining in a 

 stove.) In consequence, his chemical categories of haslc 

 colours and acid colours fail to correspond always in ■praniice 

 to the technical categories of chromatin stains and j)^'^'"^^''''^ 

 stains. 



For instance, orange is an acid colour ; but used as a 

 regressive stain I find it will give a very sharp stain of 

 chromatin : it cannot, therefore, be classed as a mere plasma' 

 stain, though it is also a very good plasma stain. Saure- 

 fuchsin is a very acid colour. It behaves in general as a 

 decided plasma stain. But used as a regressive stain it 

 sometimes, under conditions which I am not able to specify, 

 gives a very vigorous stain of chromatin. Safranin is a 

 basic colour, but by the use of appropriate mordants it can 

 be made to behave as a plasma stain. Methylen blue is a 

 basic colour. But, as is well known, when employed according 

 to the method worked out by Ehrlich for the so-called ivtra- 

 vitam staining of nerves, it affords a stain that is essentially 

 plasmatic, such staining of nuclei as may occur in this 

 process being an accidental epiphenomenon. Nigrosin is, 

 according to Ehrlich, an acid colour, and should therefore be 

 essentially a plasma stain. Yet I' find that, used as a 

 regressive stain in the same way as safranin, it gives a 

 vigorous chromatin stain, cytoiDlasm being only faintly 

 coloured. Bordeaux is an acid colour, but it stains chro- 

 matin as well as cytoplasm. Further, both carminic acid 

 and hjematein are acid dyes, but combined with the mordant, 

 alum (as in alum-carmine Or alum-h£ematoxylin), the^^ give 

 nuclear stains. Indeed, it is not too much to assert that 

 there is hardly any colour, either basic or acid, that may not 

 be made to afford either a chromatin stain or a plasma stain, 

 according to the way in which it is employed. There is, 

 in practice, no ahsolute chromatof)hily of tissue-elements. 



205. Substantive and Adjective Staining; Mordants.— In the 



industry of dyeing, colouring matters are divided into t\^ o 

 classes, according to their behaviour with respect to the 

 material to be dyed. Certain dyes are absorbed directly 

 fi'om their solutions by the material immersed therein, and 



