ME THODS OF OBSER VING BA CTERIA. 1 5 1 



III. Glycerin-Gelatin. — As the penetration of the tissue 

 by celloidin is attended with lessened staining-qualities of 

 the tubercle bacillus, it has been recommended by Kolle ' 

 that the tissue be saturated with a mixture of glycerin, i 

 part; gelatin, 2 parts; and water, 3 parts; cemented to a 

 cork or block of wood, hardened in absolute alcohol and 

 cut as usual for celloidin with a knife wet with alcohol. 



For staining bacteria (other than the tubercle and 

 lepra bacilli) in tissue, two universal methods can be 

 recommended: 



Loffler's Method. — The cut sections of tissue are 

 stained for a few minutes in Loffler's alkaline methylene- 

 blue solution (q. v.\ and then differentiated in a 1 per 

 cent, solution of hydrochloric acid for a few seconds. 

 The section is subsequently dehydrated in alcohol, cleared 

 up in xylol, and mounted in balsam. 



Pfeiffer's Method. — The sections are stained for one- 

 half hour in diluted Ziehl's carbol-fuchsin (q. v.), then 

 transferred to absolute alcohol made feebly acid with 

 acetic acid. The sections must be carefully watched, 

 and as soon as the original, almost black-red color gives 

 place to a red violet color the section is removed to 

 xylol, where it is cleared preparatory to mounting in 

 balsam. 



For ordinary work the following simple method is 

 recommended: After the sections are cut the paraffin 

 must be, and the celloidin had better be, removed. 

 From water the sections are placed in the same watery 

 stain used for cover-glasses and allowed to remain five 

 to eight minutes. They are next washed in water for 

 several minutes, then decolorized in 0.5-1 per cent, 

 acetic-acid solution. The acid removes the stain from 

 the tissues, and ultimately from the bacteria as well, 

 so that one must watch carefully, and as soon as the 

 color almost disappears from the sections remove them 

 to absolute alcohol. At this point the process may be 

 interrupted to allow the tissue-elements to be counter- 



1 Fliigge's Mikroorganismen. 



