DIT. I 



THALLOPHYTA 



373 



marsh bacteria (Fig. 296 /) in the absence of oxygen form marsh-gas and hydrogen 

 from cellulose. Bacillus protcus is the most common cause of decomposition of 

 meat, albumen, etc. 



Streptococcus (Leuconostoc) mesenterioides (Fig. 297) causes fermentation of 

 beet-sugar. It forms large mucilaginous masses like frog-spawn, the bead-like 

 rows of cells being surrounded by a gelatinous investment. The latter is not 

 formed in media from which sugar is absent. 



The Purple Bacteria, which develop in water containing decomposing organic 

 matter in the absence of oxygen and the presence of light, contain, according to 

 MOLISCH ( 4 ), a green and a red pigment (bacterio-chlorin and bacterio-purpurin). 

 Other bacteria secrete pigments in their cells or around them. The latter is 

 the case with Bacillus prodigiosus, the ellipsoid peritrichous rod-shaped cells of 

 which form fuchsin - red colonies on milk or bread, and so have given rise 

 to the miracle of the bleeding Host. 



Fio. 296. Bacteria of fermentation, a-c, Vinegar bacteria ; o, Bacillus aceti ; b, Bac. Pasteurianus ; 

 c, Bac. Kittzingianus; cl, Bac. acidi lactici, lactic acid bacillus; e, Clostridium butyricum, 

 butyric acid bacillus ; /, Plectridium paludosum, fermentation bacterium from marsh water. 

 (x 1000. From A. FISCHER, Varies, iiber Bacterien.) 



The photogenic bacteria produce within their cells a substance which becomes 

 phosphorescent on oxidation. The most widely spread of these phosphorescent 

 bacteria ( 5 ) is Bacterium phosphoreum, which occurs on meat. 



Certain soil-bacteria (Clostridium Pasteurianum, Azotobacter chroococcum) and 

 marine bacteria are able to assimilate free nitrogen. To these nitrogen-fixing 

 forms also belong Bacillus (Rhizobiuni) radicicola and Bacillus Beijerinckii which 

 live symbiotically in the root-nodules of the Leguminosae (Figs. 251, 252). 

 Mycobacterium Rubiacearum is similarly symbiotic in the leaves of tropical Rubia- 

 ceae and produces analogous bacterial galls ( 6 ). On the other hand, de-nitrifying 

 bacteria, which decompose nitrates and nitrites with liberation of free oxygen, 

 occur both in the soil and in the sea (cf. p. 276). 



The parasitic bacteria inhabit both animals and plants causing bacterioses. 

 Bacillus turncfaciens, discovered by Smith, gives rise to the cancer-like tumours 

 of Crown-gall on the higher plants. This organism is also pathogenic to man. 

 Another example is Bacillus phytophthorus, which attacks the potato ( 7 ). 



The numerous pathogenic Bacteria are the most important causes of infectious 

 diseases. Their injurious influence on the tissues and blood of men and animals 



