68 ACTIVITIES OF BACTERIA. 



The fluorescent pigments which occur in the cultures 

 of very many bacteria are identical, according to recent 

 investigations by K. Thumm. The pigment which I 

 propose to call bacterio=fluorescein, when dry, is lemon- 

 yellow and amorphous. It is soluble in water and dilute 

 alcohol, insoluble in strong alcohol, ether, and carbon 

 bisulphid. The aqueous solution, when concentrated, is 

 orange; when diluted, pale yellow. The solution, when 

 acid in reaction, presents no fluorescence; when neutral, 

 a blue; and when alkaline, a green fluorescence. In the 

 culture the fluorescence is at first blue, and later, be- 

 cause of the ammonia produced by the bacteria, becomes 

 green. The pigment is not sensitive to oxidizing agents. 

 Colorless antecedents (leuko-bodies) are not observed. 

 Phosphoric acid and magnesium appear to be essential for 

 the production of bacterio-fluorescein. (See also E. 0. 

 Jordan, Botanical Gazette, xxvii, 19. ED.) 



We have more exact knowledge concerning the beauti- 

 ful blue crystalline pigment, pyocyanin (C 14 H 14 N 2 0). It 

 can be easily extracted from cultures of the Bact. pyocy- 

 aneum with chloroform, and separated from the bacterio- 

 fluorescein. Thumm has entirely overlooked it. 



Black=growing varieties of bacteria have been but little 

 studied. According to Marpmann (C. B. L. iv, 21), the 

 black color is usually (always) dependent upon a gran- 

 ular secretion of sulphid of iron. It is thus easily under- 

 stood wliy the "pigment-production" stops upon trans- 

 ferring to nutrient media free of iron. The almost black 

 forms of the Bact. cceruleum are, however, certainly not 

 colored by sulphid of iron (Lehmann). 



There have been many investigations regarding fluctua- 

 tion of the chromogenic function. All possible in- 

 fluences which affect the growth of the bacteria unfavorably 

 also lessen the production of pigment. After con- 

 tinued cultivation upon unfavorable media or at unfavor- 

 able temperature, etc., the chromogenic function of the 

 descendants may remain permanently reduced. Thus, 

 there occur, for instance, examples of the Bact. syncy- 

 aneum which no longer produce a trace of pigment in 

 agarand milk (compare Behr, C. B. vm, 485), but which 

 color potato darkly in the neighborhood of the culture. 



