VITAL ACTIVITIES OF BACTERIA 141 



decide whether an organism possesses active independent 

 movement or is exhibiting pronounced Brownian or molecu- 

 lar motion, i. e., the dancing and tremor exhibited by finely 

 divided inorganic particles. Actual motility of an organism 

 is determined by its passing from one place in the field to 

 another. A number of organisms that are non-motile have 

 been described as possessing motility. Thus, Bact. mallei, 

 which exhibits very pronounced dancing movements, was 

 first described as being motile. The degree of activity ex- 

 hibited by certain bacteria varies according to the age of 

 the culture and the media. Such organisms as B. tetani and 

 the bacillus of black leg while exhibiting active motility in 

 the vegetative stage do not usually show such motion after 

 spores develop. It has been reported by one observer at 

 least that the degree of motility is influenced by the tempera- 

 ture at which the organisms are grown. Ferrier x has shown 

 that the motility of B. coli almost ceases and that the flagella 

 are not present w^hen this organism is cultivated at its max- 

 imum temperature, i. e., at 43 C. His explanation is that 

 the flagella under the influence of the heat form a protective 

 coat for the bacilli. 



Pigment production. So far as known the production 

 of pigment has no connection with the pathogenesis or 

 virulence of bacteria, although the pathogenic bacteria con- 

 tain a very few pigment producing organisms. Pigment 

 production, however, is an interesting phenomenon and of 

 value in the identification of certain species. The pigments 

 have not until recently been studied to any extent chemically. 

 Numerous experiments have been made to determine the 

 cause of the variation in the chromogenic function of bacteria. 

 All unfavorable life conditions such as improper media, too 

 low or too high a temperature, tend to decrease the produc- 

 tion of pigment. B. prodigiosus produces little or no pig- 

 ment when grown at 30 C. Ps. pyocyaneus does not pro- 

 duce pigment when grown under anaerobic conditions. Sev- 

 eral varieties of pigment are produced. 



1 Ferrier. Archiv de Med. Exp. et d'Anat. Path., Tome VII (1895) 

 p. 58. 



