Production of Odors and Phosphorescence 53 



the conjunctiva. It formed a brilliant yellow colony 

 upon the surface of agar-agar, but colored the agar-agar 

 itself a beautiful violet. In this case the yellow pig- 

 ment was insoluble, the violet pigment very soluble and 

 diffusible through the jelly. Some organisms will only pro- 

 duce pigments in the light; others, as Bacillus mycoides 

 roseus, only in the dark. Some produce them only at the 

 room temperature, but, though growing luxuriantly in the 

 incubator, refuse 'to produce pigments at so high a tem- 

 perature. Thus, Bacillus prodigiosus produces a brilliant 

 red color when growing at the temperature of the room, 

 but is colorless when grown in the incubator. The reaction 

 of the culture medium is also of much importance in this 

 connection. Thus, Bacillus prodigiosus produces an intense 

 scarlet-red color upon alkaline and neutral media, but is 

 colorless or pinkish upon slightly acid media. Colored 

 lights seem to have no modifying influence upon the pig- 

 ment-production. Even if for successive generations the 

 bacterium be grown so as to be colorless, it speedily recovers 

 its primitive color when restored to its old environment. I * 

 have found that Bacillus prodigiosus, robbed of its color 

 for many generations by incubation, when placed in the 

 normal environment produces its original red pigment, no 

 matter what color the light thrown upon it. Some of the 

 pigments perhaps most of them are formed only in the 

 presence of oxygen. 



7. Production of Odors. Gases such as H 2 S and NH 2 

 have sufficiently characteristic odors. There are, however, 

 a considerable number of pungent odors which seem depen- 

 dent upon odoriferous principles independent of any gases. 

 Many of them are extremely unpleasant, as that of the 

 tetanus bacillus. The odors seem to be peculiar individual 

 characteristics of the organisms. 



8. Production of Phosphorescence. Cultures of Bacil- 

 lus phosphorescens and numerous other organisms are dis- 

 tinctly phosphorescent. So much light is sometimes given 

 out by gelatin cultures of these bacteria as to enable one to 

 see the face of a watch in a dark room. Gorham found 

 the photogenesis most marked when the organisms are grown 

 in alkaline media at room temperature. Most of the phos- 

 phorescent bacteria are found in sea-water, and are best 

 cultivated in sea-water gelatin. Some are familiar to 



* "University Medical Magazine," July, 1894, vol. vi, No. 10, p. 675. 



