260 The Microscope. 



other reagents. (4) The combination of anilin dyes with each 

 other and with metal salts. (5) The combination of the gold 

 and silver methods. Not the least important and interesting 

 part of the articles is the historical description of the develop- 

 ment of the employment of anilin dyes in staining technique, 

 commencing with mail vein and fuchsin in 1850. The author well 

 observes that those who are engaged in histological research with 

 the aid of staining materials should be thoroughly acquainted 

 with the chemistry of the dyes with which they work, and a de- 

 scription is given of the source, manufacture and properties of 

 the anilin dyes as well as alixarin, logwood, indigo, carmine and 

 others. 



In his concluding article, Dr. H. Gierke has drawn up elab- 

 orate tables respecting the anilin pigments. The first table gives 

 the ordinary nomenclature, chemical formulae, remarks on the 

 solubility, reaction, and preparation of the various anilin stains. 

 The second table, arranged according to colour, gives the solu- 

 bility in water or alcohol and the behaviour with acid and 

 alkalis. 



The rest of the paper is chiefty occupied with a discussion 

 as to whether, when a preparation becomes coloured, the colour 

 is due to imbibition of pigment, or is the result of chemical 

 changes effected in the tissue by the pigment. The author main- 

 tains that though histological staining depends for the most part 

 on the physical processes of diffusion and imbibition, the occur- 

 rence of chemical combination in staining cannot be denied. 

 On the contrary, such combinations are of frequent occurrence 

 and, as micro-chemical reactions, are of the greatest importance. 

 The histological stain, so far as it imparts a permanent dye, de- 

 pends on the physical process of surface attraction. Chemical 

 processes should be suspected when a pigment is discharged or 

 changes to a different shade. We may, therefore, speak of 

 chemical processes when one and the same pigment stains dif- 

 ferent tissue elements of a preparation in different ways. Double 

 staining by the simultaneous or consecutive use of several dyes 

 only in parts depends on chemical processes. In greater meas- 

 ure they are effected by the unequally developed attraction-force 

 of various tissues. It is also shown by the fact that one pigment 

 is able to remove another from certain tissue elements, but not 



