McKenney — On Luminous Bacteria. 225 



week. Aside from the various protein-free media of Cohn, Fraenkel, 

 Gamaleia, Niigeli, Pasteur, Proskauer and Beck, and Uschinski, a large 

 number of original synthetic media, free from protein, were devised. In 

 almost all instances negative results were obtained, and hence it will be 

 needless to detail all of the synthetic protoin-free media employed. 



In the following two media, growth was at times, although not always, 

 obtained: 



I. II. 



Protogen, \%. Protogen, \%. 



NaNOg, H. Glycerol, \%. 



in distilled water. Glucose, \%. 



NaNOj, \<fo. 

 in distilled water. 



In both of these media growth was slight and after 3 or 4 days entirely 

 ceased. In no case, however, was any luminescence evident. The 

 growth in medium I. was better than that in II. Protogen which formed 

 the basis of these media is, however, a complex substance, the compo- 

 sition of which is hardly understood, and it may prove to be a protein 

 compound. 



While media containine: peptone and needed inorganic salts will per- 

 mit growth and luminescence, still the addition of certain amides causes 

 a more luxuriant growth. These amides include asparagin, lactamid, 

 isobutylamin, isovaleramid, and glycocoll. Asparagin is considered by 

 Beijerinck to be specially stimulating to luminescence. In my exper- 

 ience, while it very much promoted growth, it did not cause the least 

 increase in the intensity of the light produced. Leucin, tyrosin, and 

 sodium asparaginate were apparently without effect. On the other hand, 

 methylamin, hexamethylamin, hexamethyltetramin, uric acid, hippu- 

 ric acid and alanin,.all nitrogen containing compounds, were injurious 

 since they either retarded growth and light production or entirely pre- 

 vented growth. 



The inorganic nitrogen compovinds as a rule did not prove plastic or 

 photogenic. Among ammonia compounds, only the valerianate accel- 

 erated growth; it did not, however, affect the light intensity. The fol- 

 lowing ammonium compounds proved either injurious or at least indif- 

 ferent: — tartrate, bimalate, chloride, carbonate, nitrate, sulphate, phos- 

 phates, and aldehyde-ammonia. 



Nitrate of sodium proved not alone plastic but particularly photo- 

 genic. The nitrates of potassium, lithium and calcium proved neither 

 plastic nor photogenic. 



In none of the synthetic media containing peptone, amides and inor- 

 ganic salts, in which distilled water was used as the solvent, was the 

 growth nearly as good as when, in place of the distilled water, fish ex- 

 tract was used as the solvent for the peptone, amides and inorganic 

 salts. Evidently, while peptone may be an essential organic constituent 

 of the nutrient media, it alone or with any of the plastic nitrogen com- 



