216 McKenney On Luminous Bacteria. 



stability of the cultures and permitted access of free oxygen to all parts 

 of the media. 



Relations to Acids and Bases. 



In his study of Bacterium phosphor escens, Beijerinck came to the con 

 clusion that certain acids, e. g. lactic, malic, glyceric and aspartic, ac 

 celerated light production, while others, such as formic, acetic, propionic 

 and butyric decreased light emission. Still others, e. g. citric, mucic. 

 oxalic and glycolic, appeared to be without effect on the bacterium. 

 Beijerinck further observed that certain of the salts of these acids reacted 

 toward the bacteria much as did the free acid. That free acids should 

 in all cases prove injurious, or even that they should all be beneficial, 

 would not be particularly surprising, This variation in the action of 

 the acids was, however, difficult to understand. 



A quantity of normal fish bouillon, agar, and gelatine were made 

 weakly acid with HC1, HNO f , HjPO ? and CH^COOH respectively. 

 These media were then inoculated with Bacillus phosphorescens and 

 Bacterium phosphorescens; but no growth ever appeared. Since the 

 acid might perhaps inhibit initial, but not later growth, and not the 

 light production, luminous cultures were obtained in normal media and 

 the acids then added. 



To a stab gelatine culture of Bacterium phospJiorescens, 4 drops of 

 decinormal HC1 were added with a pipette. The acid was dropped 

 directly on the bacterial growth. The light was instantly extinguished. 

 During the 6 hours following treatment no light was emitted, but after 

 24 hours a faint light was visible in the culture. This experiment was 

 repeated a number of times and each time with the same result. Evi 

 dently the acid was injurious to light production, but not for the life of 

 the organism. 



In a second series of experiments, cultures in normal fish bouillon 

 were employed. To such cultures, which were strongly luminous, 4 drops 

 of decinormal HC1 were added. No effect on light emission was ob 

 served. Examination showed that the amount of HC1 added had not 

 been sufficient to give the medium an acid reaction. Decinormal HC1 

 was then added to another lightning bouillion culture until the light 

 emission ceased. The culture fluid was then found to be slightly acid to 

 litmus paper. 



Normal, double normal, and fairly concentrated HC1 were in turn 

 added to a series of light-emitting bouillon cultures until the light disap 

 peared. In each case the media at the end of the experiment were 

 slightly acid to litmus. Naturally the more concentrated the acid the 

 less was required to cause cessation of light production. In no case, 

 however, did the light disappear until the media became slightly acid. 

 The experiments were repeated in bouillon cultures containing litmus. 

 In all cases light disappeared as soon as the medium turned faint red, 

 i. e., was acid, and not before. 



One may interpret the difference between the results obtained with 

 solid and fluid cultures by the fact, that with the solid media the acid 

 acted at once on all of the bacteria, while in fluid culture only some of 



