140 ESSAYS ON BACTERIOLOGY. 



intestinal canal and genito-urinary organs, may be 

 cleared up. 



It is probably in tuberculosis that bacteriological 

 diagnosis has won its most striking and complete tri- 

 umph. The frequency and seriousness of the disease, 

 and the importance of its early recognition, combine 

 to render this triumph the more noteworthy. It may 

 fairly be said that, by the skillful use of the means 

 now available, the diagnosis of tuberculosis, even in 

 its early and obscure forms, is almost completely com- 

 passed. 



The microscopic identification of the tubercle ba- 

 cillus is made possible by its almost peculiar staining 

 reaction. It stains only with difficulty, but, being 

 stained, resists decolorizing agents more than other 

 bacteria. To this rule there are but few exceptions, 

 and those, with care, readily recognized in ordinary 

 work. Many methods, differing in details, and all 

 based upon the rule just stated, have been devised for 

 staining the tubercle bacilli. But few of them are in 

 common use. In the original Koch-Ehrlich method 

 anilin oil was iised as a mordant. Carbolic acid has 

 been found to answer a similar purpose. The stain- 

 ing solution now generally used is called Ziehl's car- 

 bol-f uchsin, being made as follows : To distilled wa- 

 ter is added 5 per cent, of crystallized carbolic acid, 10 

 per cent, of alcohol, and 1 per cent, of dry fuchsin. 

 After complete solution of the solids, and filtration, it 

 is ready for use. Decolorization is accomplished by 



