56 PATHOGENIC BACTERIA. 



pungent oders which seem dependent purely upon odor- 

 iferous principles dissociated from gases. Many of them 

 are extremely unpleasant, as the onion-like odor of the 

 tetanus bacillus. The odor does not have any direct rela- 

 tion to decomposition, but, like the colors and acids, 

 seems to be a peculiar individual characteristic of the 

 metabolism of the organism. 



8. Production of Phosphorescence. A Bacillus phos- 

 phorescens and numerous other organisms have a dis- 

 tinct phosphorescence associated with their growth. It 

 is said that so much illumination is sometimes caused by 

 a gelatin culture of some of these as to enable one to tell 

 the time by a watch. Most of them are found in sea- 

 water, and are best grown in sea-water gelatin. 



9. frodnclion of Aromatics. The most important of 

 these is indol, which was at one time thought to be pecu- 

 liar to the cholera spirillum. For the method of deter- 

 mining its presence, see "Dunham's Solution." At pres- 

 ent we know that a variety of organisms produce it, and 

 that it and phenol, kresol, hydrochinon, hydroparacumaric 

 acid, and paroxy-phenylic-acetic acid are by no means 

 uncommon. 



10. Reduction of Nitrites. A considerable number of 

 bacteria are able to reduce nitrites present in the soil or 

 in culture-media prepared for them into ammonia and 

 nitrogen. To the horticulturist this is a matter of much 

 interest. Winogradsky has found a specific nitrifying 

 bacillus in soil, and asserts that the presence of ordinary 

 bacteria in the soil causes the reduction of no nitrites so 

 long as his special bacillus is withheld. 



1 1. Peptonixation of Milk. Numerous bacteria possess 

 the power of digesting peptonizing the casein of milk. 

 The process differs with different bacteria, some digesting 

 the casein without any apparent change in the milk, 

 smiie producing coagulation, some gelatinization of the 

 fluid. In sonic cases the digestion of the casein is so 

 complete as to transform the milk into a transparent 

 watery fluid. 



