44 TEXT-BOOK OF BACTERIOLOGY. 



On the other hand, the combination of coloring matters belong- 

 ing to the basic anilin group with a particular kind of mordant is 

 extremely useful for bacterial researches, by disclosing the finest 

 peculiarities of form. The staining of the flagella by Loffler's 

 method is effected by treating the preparations with a compound 

 mordant fluid. This consists of two parts say 10 cm. of a 20-per- 

 cent solution of tannin, a few drops of saturated aqueous solution 

 of ferro-sulphate, and one part say 4 or 5 cm. of an infusion of 

 logwood, taking one portion of wood to 8 of water. This gives an 

 inky fluid; and in fact, Loffler was led to the discovery of his 

 method by employing black ink as recommended by Neuhaus. 



There are two other substances which act as mordants, though 

 they do not belong to that group, namely, anilin oil and phenol, 

 with their allies. 



Anilin oil (the mother of most of the anilin colors) is an oily 

 body of peculiar smell, obtained from tar. It is not a genuine oil, 

 but rather, by its chemical composition, a mere derivative of the 

 combination with the aromatic series of benzol, and it took its name 

 only from its outward behavior. It is employed in aqueous solution, 

 and in connection with it gentian-violet and fuchsin yield extremely 

 valuable stains which we often have to employ. There are nu- 

 merous directions given for uniting such an anilin coloring solution 

 with a saturated aqueous oil solution. 



The latter is thus obtained : take 5 cm. of anilin oil and skake 

 it well for some minutes with 100 cm. of distilled water, and pass 

 it through a moistened filter. The filtered fluid must be as clear 

 as water, must show no more oil-drops, and must not become tur- 

 bid when shaken. 



Yet this anilin water, as it is often called, is not stable. It is 

 apt to decompose, and even the addition of alcohol, as has been 

 recommended, only remedies this defect to a certain degree. It is 

 therefore much better to prepare a small quantity of fresh anilin 

 water for every new requirement. In this way one is surest to 

 avoid deposits and faults of staining. Pour anilin oil into an empty 

 test-tube to the depth of about 2 cm., add distilled water, shake up 

 for a few moments, filter the emulsion, pour the clear results of this 

 filtration (which have a strong smell of anilin oil) into a glass dish, 

 and then add as much of a concentrated alcoholic solution of fuch- 

 sin or gentian-violet, or other coloring matter, as is required to 

 produce saturation with coloring matter. This is easily recogniza- 

 ble on the surface by the appearance of a peculiar iridescent film 

 with metallic colors, which consists of undissolved coloring matter 

 and shows the state of saturation. In many cases, however, it is 



