272 ACID FUCHSINE. 



The experiments made with the spirilla will be the subject of 

 another communication. 



Aqueous solutions of acid fuchsine (fuchsine, S. Griibler) have 

 been found to be excellent indicators for acids and alkalies. 

 Solutions of this aniline dye lose their bright red colour in the 

 presence of alkalies, and recover it or become more intensely red 

 when acted upon by acids, either mineral or vegetable. It has 

 been found out that o'oi of a centigramme of caustic potash 

 combines with 0*005 ^^ ^ milligramme of acid fuchsine, and 

 forms a colourless salt, the sensibility of which is that o"oooo3 of 

 a gramme detects o'ooi of a cubic centimetre of pure hydro- 

 chloric acid. The intensity of the colour assumed by the indica- 

 tor is directly in relation to the amount of the reagent. Moreover, 

 so far as has been observed, the addition of acid fuchsine to the 

 culture media has not the slightest influence on the growth of the 

 germs. To ten cubic centimetres of ordinary bouillon more than 

 o"5 of a cubic centimetre of a saturated aqueous solution of acid 

 fuchsine was added without inhibiting the growth. This indicator 

 has the advantage of being readily soluble in water ; the solutions 

 are entirely clear and transparent, and do not produce precipitates 

 when the medium is rendered sufficiently alkaline to completely 

 decolourise it. This is quite in contrast with other aniline colours, 

 which have more or less these properties. It is known that 

 Legrain used solutions of ordinary basic fuchsine for the same 

 purpose. This has not in the author's hands yielded good results, 

 because it is far less sensitive than acid fuchsine ; the solutions 

 are cloudy, and throw down a brownish-red precipitate in the 

 presence of alkalies, which interferes with the tests. 



These tests include many kinds of media, to which has been 

 added the acid fuchsine, viz., ordinary peptone bouillon, beef tea, 

 Dunham's peptone solution, Dunham's peptone solution with 

 glycerin, somatose solutions, and somatose solutions with glycerin ; 

 also these media to which agar-agar and gelatin had been added. 

 Of each medium two specimens were prepared, one pink, and the 

 other decolourised, the difference being that the pink was exactly 

 neutral in its reaction, while the so-called decolourised was slightly 

 alkaline. The amount of acid fuchsine in both was about the 

 same. 



