490 Dr. Bolley on the Theonj of Dyeing. 



matters, indigo for example (called for this reason a substantive 

 dye), possess this affinity so strongly that even the employment 

 of a mordant may be dispensed with ; nothing then can be more 

 natm'al than to expect something similar in the process of colour- 

 ing microscopic objects, and to explain the colouring effect of any 

 pigment on the cell-nucleus simply on the ground of the chemical 

 affinity between the substance of the nucleus and the di/e employed. 



"That chemical affinities do here, in fact, come into play, may 

 be gathered a priori from the fact that other granular or vesicular 

 contents of the cells, morphologically similar, but of a different 

 chemical constitution, do not unite with pigments; and the jus- 

 tice of this view will appear more clearly with regard to each 

 separate kind of material in the cou.rse of the present work. 



" The physical state of the material to be coloured does not, 

 however, appear to me to be altogether without effect. Besides 

 chemical affinity, surface attraction, as it is exhibited in charcoal 

 and platina, certainly contributes in some cases to the result, by 

 rendering the effect of the former more considerable. 



" 1 have addressed the following experiments in the first place 

 to discover those physiologically important substances in which 

 the power of attracting colour is innate ; but as it is well known 

 that nitrogenous substances, such as wool and silk, are especially 

 fitted for dyeing, so I have begun the series of my experiments 

 with this group, or rather with the group of proteine substances." 



Maschke then describes a series of observations of his own, 

 from which we shall select such as seem to relate to our subject. 



Of horny tissue, for example, he says, " The power which 

 horny matter possesses of attracting colour is well known to 

 dyers. I was therefore the more surprised at finding, on repeated 

 and most carefully conducted experiments, hardly a trace of colour 

 in hair and wool which had been treated with ether, even after 

 they had laid for hours in the dye-bath. Only where the fibres 

 had been cut or broken, or where, through pressure or friction, 

 the external surface of the hair had been abraded so as to expose 

 the corticular substance to the operation of the dye, did the 

 colour after long exposure begin to become visible. 



"This paradox disappeared when tlie temperature of the 

 coloured solution containing the object under microscopic exami- 

 nation was greatly elevated ; then the process of colouring was 

 seen to proceed from the sections of the hairs, to enter their ex- 

 tremities, and thence to spread over their entire lengths. It 

 seems, therefore, that the phajnomenon first noticed results from 

 the external covering of the hair opposing itself obstinately to the 

 entrance of the coloured liquid ; and that in aqueous solutions 

 at ordinary temperatures, both this external covering and the 

 corticular substance become soaked but very slowly." 



