BACTERIA. 255 



4. Gram's Method. 



470. The so-called Gram's method is adapted especially 

 for sections, because it stains the Bacteria in them deeply 

 without staining the nuclei at the same time. But it may 

 also be used with cover-glass preparations, especially if they 

 contain many other stainable bodies besides Bacteria. 



According to Gram's original account, this method con- 

 sisted in placing the sections first for several minutes in 

 Ehrlich's aniline-water-gentian-violet solution ( 469), and 

 then transferring them to a solution containing one part of 

 iodine and two parts of potassium iodide in 300 parts of 

 water. After a few minutes in this, they are washed with 

 alcohol until no more color comes off, then transferred to 

 clove-oil, which removes more of the dye, and finally mounted 

 in balsam. 



471. But, according to Giinther (I, 89), it is better, in 

 most cases, to treat the sections, after removal from the 

 iodine solution, for half a minute with alcohol, thenyktf ten 

 seconds* with 3$ hydrochloric acid-alcohol, and then at 

 once with pure alcohol until they are completely decolor- 

 ized. For transferring them from alcohol to balsam, this 

 author recommends xylol, instead of clove-oil. 



According to the method described by Weigert, aniline 

 is gradually dropped upon the sections, differentiating and 

 dehydrating them, and they are then passed through xylol 

 into balsam. 



472. A sharp double staining, by which the nuclei are 

 differently stained from the Bacteria, may be obtained by 

 preliminary staining with picro-carmine ( 318). This solu- 

 tion is allowed to act one or two minutes on the sections, 

 which are then carefully washed with water, placed in 

 alcohol, and finally stained again according to the Gram or 

 the Gram-Gunther method. 



* For pretty thin paraffine sections this time is certainly too long. 



