OPTICAL ACTIVITY. 57 



does not depend upon oxidation of a photogenic substance 

 separated from the bacteria (K. B. Lehmann and Toll- 

 hausen, C. B. v, 785). Everything that interferes with 

 the life of the bacteria, lessens it also ; cold makes the or- 

 ganisms rigid, and interrupts the ^phosphorescence while it 

 continues. High temperature, acids, chloroform, etc. , dis- 

 turb the light-phenomenon momentarily. Living cultures 

 may always be obtained by inoculating from cultures that 

 emit light. The germ-free filtrate never gives light. 

 While no light is given off except when the bacteria are 

 alive, still the live bacteria do not necessarily emit light; 

 for example, in an atmosphere of C0 2 . Similarly, a mus- 

 cle can not contract except it is alive, but may be alive 

 without contracting. (Compare also Suchsland, C. B. L. 

 iv, 713.) 



According to Beijerinck (C. B. viii, 616 and 651), all light-giv- 

 ing bacteria, which he places in a (physiologic) "genus," photo bac= 

 terium, require peptone and oxygen in order to emit light. Two of 

 his varieties are satisfied with this ; the four others require, besides 

 peptone, also a source for carbon, which may also contain nitrogen. 

 As such, small quantities of sugars (dextrose, levulose, galactose, partly 

 maltose) and glycerin, as also asparagin, are suitable. A higher pro- 

 portion of sugar, because of marked fermentation and production of 

 acid, stops the emission of light in some cases. As for salts, 3% to 4% 

 of sodium chlorid is favorable, magnesium chlorid appears to promote 

 the production of light still more, while sea-salt is best. 



To preserve the photogenic function it is best to em- 

 ploy a gelatin nutrient medium, which is prepared from 

 an infusion of fish in sea-water (or artificial sea- water con- 

 taining 3% of sea-salt) with the addition of 1% of peptone, 

 1 % glycerin, and 0. 5 % asparagin. But even on this me- 

 dium, if the transfer is infrequent, the ability to produce 

 light is soon lost, so that the cultures found in laborato- 

 ries are not usually photogenic. By repeated frequent 

 transfer to suitable media the photogenic property may 

 often be regained. I employ two salt herrings, cooked in 

 a liter of water, and, after filtering, add 10% gelatin with- 

 out neutralization. 



