THE BACTERIA 



279 



cells of the filament become isolated for reproductive 

 purposes, forming motile cells or zoospores (see Fig. lllA), 

 which pass through a swarming stage, possessing a lateral 

 tuft of cilia. Endospores are not found in any of these 

 forms, but in some of them, as in Crenothrix (Fig. Ill, 

 B and C), the contents of the cells may divide up into 

 numerous small swarm-cells 

 or microzoospores. The re- 

 lations of these organisms to 

 the typical Bacteria, as re- 

 presented by B. subtilis, is 

 quite an open question, 

 though on the other hand 

 their affinity to the Cyano- 

 phycese seems rather closer. 

 Before leaving the Bac- 

 teria, it may be mentioned 

 that while the great ma- 

 jority are either saprophytes 

 or parasites, a few have 

 been found capable of de- 

 riving their food entirely 

 from inorganic substances. In some of these cases carbon- 

 dioxide is decomposed under the influence of light, with 

 the help either of true chlorophyll or of a purple pigment 

 which seems to have similar functions. Another member 

 of the group is able to obtain its carbonaceous food from 

 inorganic carbonates without the aid of light,- a power 

 possessed by no other organisms at present known. The 

 same Bacteria in which this remarkable property resides 

 are of great importance in another respect, as they bring 

 about the oxidation of nitrogen, thus forming the nitrates 

 in the soil. 



FIG. Ill A. Cladothrix diehotoma. 

 Part of a branched filament, 

 showing formation of ciliated 

 swarm-cells. x 1000. (After 

 A. Fischer.) 



