180 McDermott — Observations on a Photogenic Micro-organism. 



gradually weakens, owing to the drying of the medium, and 

 finally dies out; the maximum intensity of light is about 48 

 hours after inoculation. 



Agar cultures appear to grow about as well as gelatin cultures 

 but luminesce weakly or not at all, even in the presence of the 

 proper amount of mineral salts. Liquid media of very simple 

 composition serve for the growth of the organism ; the simplest 

 medium serving for luminosity is a 3.0 per cent solution of 

 salt, containing 1.0 per cent of asparagin.* This medium is of 

 course not the best; cultures in it are short-lived, and glow 

 only feebly; a better medium is — 



Sodium chloride 2.5% 



Magnesium chloride 5 



Peptone 1.0 



Asparagin 1.0 



Glycerin > - .5 



Larger amounts of peptone and asparagin act adversely to 

 growth; the organism is apparently sensitive to " over-feeding." 

 It will grow and luminesce in milk containing 3.0 per cent of 

 common salt; the light on the surface is quite bright. As a 

 rule, however, the light from luminous cultures is much less 

 intense than that from gelatin, though when shaken gently, 

 the light perceptibly increases in intensity. The mineral salt 

 present may be any one of several, but the brightest cultures 

 have been obtained by the use of 2.5 per cent of sodium nitrate, 

 and 0.5 per cent of magnesium chloride. All media must be 

 faintly alkaline to litmus. 



The spectrum of the light emitted by a gelatin culture is of 

 very limited range, extending from the yellow-orange to the 

 indigo, with a decided maximum intensity in the green. This 

 spectrum is of less extent than that of our local fireflies (Photi- 

 nus pyralis, Photuris pennsylvanica, etc.) although the appear- 

 ance of the light to the eye does not differ so very much from 

 that of the last-mentioned Lampyrid. In liquid cultures the 

 light appears to the eye to be more whitish, though the range 

 of the spectrum is the same; probably the maximum intensity 

 is shifted to a different point. 



* In this connection it is of interest to note that Wood (Journ. Amer. Med. Assn., 

 1911. Vol. 56, pp. 1094-6), has recently recommended " normal " (physiologic) salt solu- 

 tion as an emergency culture medium for many bacteria. 



