McKenney — On Lxiininous bacteria. 229 



Radziszewski, Ludwig and Dubois believe in the extracellular theory. 

 The observations at hand give almost equal support to both sides of the 

 question, although the intracellular theory seems to have a little the 

 better of the argument. 



That light is an oxidation phenomenon, is pretty largely accepted by 

 all students of the luminous bacteria. The questions to be settled are, 

 however, numerous, e. g., what it is that is oxidized, the conditions of 

 oxidation, how the light is produced by oxidation, and is the oxidation 

 internal or external? We know that even in an abundant supply of 

 fresh oxygen the photobactoria may be non-luminous. Further, con- 

 tinued growth and light production do not necessarily go hand in hand. 

 We have seen that photogenic bacteria may grow at a high temperature 

 without producing light, e. g. Bacillus phosphorescens will grow at 38°, 

 but remains perfectly dark. 



A culture of Bacillus phosphorescens does not emit light as soon as the 

 first growth takes place. Usually it is not luminous until from 18 to 

 24 hours after inoculation. During this period the culture medium is 

 seen to become more and more clouded with a white growth, and finally 

 a white skin of bacterial growth covers the surface of the culture liquid. 

 Then the culture becomes luminous. This is not duo to contact with 

 the air, because when the culture is luminous, it is luminous to a depth 

 of 2 to 3 centimeters. Again we have seen how a certain amount of 

 ether may prevent light production and yet not growth. 



During the 18 hours immediately following inoculation, and before 

 luminescence begins, the bacteria are actively swimming about the cul- 

 ture liquid. After light production begins not only are the bacteria of 

 the surface skin motionless, but also those in the depths of the liquid. 

 In no case have I observed light while the bacteria were motile, and 

 conversely I have not been able to find the bacteria in motile condition 

 while they were in a luminous condition. Indeed it would seem — at 

 least for Bacillus pJiospJim-escens — that light and motion are opposing 

 functions, since they are not performed at the same time, but one follows 

 the other. 



As long as the bacteria are in motion, the culture has but little odor 

 (unless fish extract has been used) and is of a light yellow color. Shortly 

 after the culture becomes luminous, the color changes. First it becomes 

 dark yellow, then it is light brown, then more and more reddish. By 

 this lime the odor is very marked and reagents are hardly needed to 

 demonstrate the presence of the lower fatty acids and of skatole. And 

 reagents confirm the olfactory evidence. 



It has been shown' that the elements sodium and magnesium are of 

 importance for both light and growth of luminous bacteria. Just what 

 the connection may^be between the oxidation which causes light emis- 

 sion and sodium or magnesium is still a question needing further experi- 

 mentation. That there is some connection is clear. A comparison of 

 luminous bacteria with the electric ray is rather suggestive. The elec- 

 tric organ of the torpedo is known to be rich in NaCl, usually having as 

 much as 3^. Further, it is commonly accepted that the electric organ 



