The Microscope. 71 



are especially the children of modern chemistry. Like organic 

 substances, they consist mostly of charcoal or carbon, C ; oxygen, 

 O ; hydrogen, H ; and nitrogen, N, with in some cases small 

 quanties of sulphur, chlorine, or other element. The variety of 

 elements in their composition being so small, their properties 

 are due to variation in the number and peculiar grouping of the 

 atoms around a central nucleus of carbon. 



According to Giercke^, Waldeyer was the first to employ these 

 dyes in microscopy, but he says they have not yet found favor. 



This statement is no longer true, they are essential in bacterio- 

 logical work, and also in double staining, in which they achieved 

 their first success. 



Slight changes in the methods of manufacture often make 

 differences of shade which are denoted by letters as BB, BBB, or 

 4B, the latter indicating a deeper shade, or as scarlet G, (gelb) 

 orange. 



Most of our supply comes from Germany, but several kinds 

 are now made in this country. Nearly every dye is protected 

 by patents and made by a single firm. 



The chemical name of these substances expresses their com- 

 position according to chemical rules, but as the name increases 

 in length with complexity of composition, those much in use 

 often acquire trade names, that vary with the fancy of the 

 maker. Thus Bismark brown, vesuvin, anilin brown, leather 

 brown, Manchester brown, etc., are trade names of the dye 

 known to chemists as Triamido-azo-benzene chloride, C12 H15 N5 

 CI2. Chrysoidin is Diamido-azo-benzene chloride, C12 H13 N4 CI. 



From a practical standpoint, they are divided in two classes, 

 those which dye without mordants, or substantive colors, and 

 those which require some fixing agent, as chrome alum or acetic 

 acid, known as adjective colors. The substantive colors are best 

 adapted for the microscopist. 



The earlier colors had much more affinity for animal matter 

 than for vegetable, and hence were not well adapted for plant 

 work. The number of substantive dyes has lately been much 

 increased by additions to the class of azo dyes, adapted to unite 

 with cellulose without any mordant, and extremely fast to light, 

 etc. 



Among these especially to be recommended for the microscop- 



2 Gieicke, 262 methods of staining. Am. Monthly Micros. Journ. 1885-1886. 



