102 



BACTERIA AND THE NITROGEN CYCLE 



these pathological bacteria with saprogenic properties many of the fluorescent 

 and photogenic bacteria would have their place. Bacillus fluorescens lique- 

 faciens, an actively motile aquatic species, breaks down albumen into 

 peptones, fatty acids, and other compounds. One of the bacteria of the 

 intestine, described formerly as Bacillus putrificus coli, yields peptones, 

 indol, skatol, amides, and ammonia. Similar to this species in its action 

 on albumens are the toxine-forming B. vulgaris (Proteus vulgaris] and its 

 allies. B. vulgaris makes its appearance almost always in meat infusions 

 exposed to the air. It is a slender rod 1-5 4 M long by 0-5 /u, thick, with 

 a tendency to form chains. It is peritrichous and actively motile (Fig. 22). 

 Closely related to it are a number of forms (Kurth's, B. Zopfii, and others), 



FlG. 22. Putrefactive bacteria, a, Bactrillum pseudotermo, corresponds most closely to the old Bacterium termo 

 ofCohn. 6, Cholera-like vibrio from putrid water, c, Bacillus ureae. the commonest cause of urinous fermentation, 

 probably identical with Pasteur's Micrococcus ureae. d-A, Bactridium Proteus (Bacillus Proteus, Bacterium. 

 Zopfii, Proteus vulgaris, &c.)- d, peritrichous rod, cobweb-like growth (zoogloea) on gelatine (50 diam.) ; f, 

 portion of same more highly magnified (300 diam.) ; g, tree-like growth on gelatine with thickenings ; A, part of 

 same magnified 300 diam. to show the structure of thickenings which consist of closely wound threads. Magn. a-d 

 about 1500, e and ^-50, /"and A 300. 



all placed at one time by Hauser in one genus Proteus, so called on account 

 of the manifold shapes of their colonies on gelatine*. These colonies are 

 ramified zoogloeae having under a low power much the appearance of fungus 

 mycelia, covering the gelatine with a filamentous growth. Each filament 

 consists of chains of bacteria united by a jelly-like substance (Fig. 22, d-h). 

 These apparently specific putrefactive bacteria must not be looked 

 upon as an exclusive group, such as the sulphur or nitrifying organisms, 

 whose metabolism is of a circumscribed kind and which can only thrive 

 when its peculiar conditions can be fulfilled. Thevarjous species of Proteus, 

 for instance, have zymogenic as well as saprogenic properties. They can 

 ferment carbohydrates, producing gas and acid during the process, as does 

 also Bacillus coli communis. 



* See Annals of Botany, Vol. xiii, 1899, p. 198, for an account of Proteus. 



