TEXT-BOOK OP BACTERIOLOGY, 229 



discovery for so long a time. Koch found that solutions to which 

 had been added an alkali were rendered more powerful, although 

 staining slowly, and that they were not at all or only reluctantly 

 •decolored, while on the contrary all other known bacteria were 

 readily stained by this solution and just as readily decolored. 



In this way Koch first stained the bacilli with his alkaline 

 methyl-blue, whose method of manipulation has been previously 

 stated, and we will therefore at once consider the complete method 

 first described by Ehrlich. 



The essential of the Koch-Ehrlich's staining of tubercle bacilli 

 was the employment of anilin-oil water-color and the diluted acid 

 for decoloring. The basis of proceedings has remained unchanged 

 since that time, even if "in some instances deviations in technique 

 have been employed. Thus the anilin-oil mixture has been sup- 

 planted by Ziehl's carbol-fuchsin with advantage. The length of 

 time in staining cover-glasses is in general shortened through heat- 

 ing, and the concentration of the decoloring acid is somewhat les- 

 sened. 



Upon this has been constructed the method of which, because 

 of its practical importance, should be described with special accu- 

 racy, and is as follows : 



In the examination of cover-glass preparations for tubercle 

 bacilli, they must first be properly prepared before staining. For 

 this purpose pour the entire sputum into a dark glass vessel or 

 plate,* so as to recognize better its constituent parts; for we have 

 not only to examine the excretions of the diseased lung, but also 

 the mucous secretions of the upper air-passages and the saliva, and 

 as a rule it is only the lung secretion that contains the bacilli. 

 Therefore select out of the mixture on the plate one of those yellow 

 conglomerate and tough masses of mucus which undoubtedly have 

 their origin in the lung and were so recognized in pre-bacteriologi- 

 cal times as "lentils" in tubercular sputum which called for special 

 attention. Extract one with the platinum needle, put it upon 

 a cover-glass, and then place a second cover-glass upon it, just as 

 in preparing blood and film preparations. 



Through pressure upon the upper glass and sliding both glasses 

 to and fro crush the nodule and attempt to spread it between and 

 upon the glasses as evenly as possible. The latter are then care- 

 fullj' drawn apart and permitted to dry in the air, when they are 

 drawn three times through the flame and are then ready for 

 staining. 



* An ordinary soup-plate, painted a dead black, will answer. — J. H. L. 



