226 McKenney — On Luminous Bacteria. 



pounds mentioned is not sufficient to produce the best growth of the 

 organisms. 



In order to determine whether perhaps a second form of carbon supply 

 was needed, a series of sugars and related compounds were added to the 

 media as secondary- sources of carbon. When, in addition to peptone, 

 \<fo of either dextro.se, lactose, cane sugar or dulcite, was added, the 

 growth was a little more than that in the control without the sugar or 

 the alcohol. Maltose (1^) at first accelerated growth, then retarded it, 

 and later again caused acceleration. Arabinose and levulose retarded 

 both growth and luminescence, while the presence of 1^ of inulin was 

 sullicient to entirely prevent growth. The glucosides arbutin, fcsculin 

 and agaracin retarded growth or were at least indifferent in their action. 

 A nvimber of additional organic compounds were experimented with. 

 Among these protogen, lecithin, glycerol, sodium lactate, sodium phos- 

 pholactate and sodium oleinate produced increased growth, but seemed 

 without effect on light production. The following retarded growth: 

 ethyl alcohol, butter, palmitin, stearin, cholestrin, camphor, turpentine, 

 xylol, and citrus, olive, and bone oils. 



Peptone and sea-salts dissolved in distilled water constituted a medium 

 siiMicient to enable the photobacteria to produce fully as intense a light 

 as when fish or fish extract, peptone and sea salt, etc., were employed. 

 The growth was, however, never as luxuriant in the purely synthetic ■ 

 media as in the media containing fish extract. 



MINEKAL NEEDS. 



All observers have emphasized the fact that in order to insure the best 

 growth a certain amount of sea salt must be added to the culture media. 

 Be^'ond this nothing is known concerning the inorganic needs of the 

 photobacteria. One great dithculty in the way of investigating mineral 

 needs of luminous bacteria is the fact that peptone must form part of 

 the nutrient medium. All preparations of peptone contain a consider- 

 able amount of ash. Griibler's purified peptone, which was the best at 

 my disposal, contained about \<fo of ash, while the Witte peptone, which 

 was rarely employed, contains rather more than 1^. The ash of the 

 Gri'ibler peptone (that used in the following experiments) contains iron, 

 barium, sodium and potassium. Since peptone is essential, it at first 

 seemed very improbable that anything could be learned about the 

 mineral needs of the bacteria. 



The various culture media employed for preceding experiments have 

 all contained a varying number of inorganic salts. The question then 

 arose, might there not be enough mineral matter in the peptone to pro- 

 vide for its inorganic needs? Distilled water containing 1 or 2^ of pep- 

 tone, however, remained free from growth even a week after inocula- 

 tion. When, however, 2^ of sea salts was added to the 1^ peptone 

 water fairly good growth and a very strong luminescence were obtained. 

 In order to learn whether the complete mixture of salts contained in sea 

 water was necessary, or only certain of these, media were made up con- 



