METHODS OF OBSERVING BACTERIA. 91 



Rubin-pararosanilin hydrochlorate. 

 Methylized, ethylized, and benzylized 

 pararosanilid : 



Crystal violet, 



Gentian violet, 



Victoria blue, 



Methyl green, 



Auramin. 



The rosanilins are more difficult to prepare 

 than the pararosanilins, and are generally 

 mixed with them. The pararosanilins 

 color more sharply than the rosanilins. 



4. Amido-azo combinations : 



Bismarck brown, 

 Phenylene brown, 

 Vesuvin. 



5. Chinolin derivatives : 



Cyanin. 



B. Naphthalin group. Magdala red. 



The best anilin dyes made at the present time, and 

 those which have become the standard for all bacterio- 

 logical work, are made in Germany by Dr. Griibler. In 

 ordering the stain the name of this manufacturer should 

 always be specified. 



A whole volume could easily be devoted to scientific 

 staining. Indeed, the technical difficulties encountered 

 are so great that no explanations can be too thorough to 

 be useful. The special methods essential for such bac- 

 teria as have peculiar staining reactions will be given 

 with the description of the organism. General methods 

 only will be discussed in this chapter. 



Cover-glass Preparations for General Examination. 

 The material to be examir.ed must be spread in the 

 thinnest possible layer upon the surface of a perfectly 

 clean cover-glass, and dried. Here it may be remarked 

 that for bacteriological purposes thin covers (No. i) are 

 generally required, because thick glasses interfere with 

 the focussing of the oil-immersion lenses, and that cover- 



