20 PLANT PHYSIOLOGY 



isms. In the majority only organic and highly complex 

 compounds are made to yield the needed energy, but in 

 some organisms much simpler inorganic compounds suf- 

 fice, and in a few now known (more may later be dis- 

 covered) the carbon-containing compounds are not used 

 at all. 



The nitro-bacteria, as shown first by Winogradsky, * oxi- 

 dize simpler nitrogen compounds in order to liberate the 

 energy which they need, employing carbon-compounds only 

 in the synthesis of food to be used in the construction of 

 their living bodies. One set of nitro-bacteria oxidize am- 

 monia, or compounds of ammonia, to nitrous acid, the first 

 and last steps of the process being indicated by the reac- 

 tion — 



2 NH. OH + 3 0, = 2 HNO, + 4 H, 



Another set oxidize the nitrous acid, or its salts, to 

 nitric acid thus — 



2 HNO, + 0, = 2 HNO, 



The sulphur-bacteria ( Beggiatoa, etc. ) obtain most if not 

 all of their kinetic energy by oxidizing sulphur compounds. 

 Thus they precipitate sulphur in their own bodies by oxidiz- 

 ing the sulphuretted hydrogen ( H„ S ) present in the waters 

 in which they live.f If the supply of the gas remain suffi- 

 cient, the sulphur will accumulate as a reserve supply in the 

 cells ; if it decrease, the reserve sulphur will be oxidized and, 

 uniting with water, will form sulphuric acid, or its salts, 

 thus — 



S + 0, ( + Aq)=SO, (+Aq) 



2S0, + 0, (+Aq)=2S03 ( + Aq) 

 SO3 + H, (+ Aq)= H, SO, ( + Aq) 



Those bacteria {e.g. Crenothrix) which, living in water 

 rich in iron, deposit iron in some form in or upon their own 

 bodies, may obtain their kinetic energy by physiologically 



* Winogradsky, S. Eecherches sur les organismes de la nitrification. An- 

 nales de I'lnst. Pasteur, IV., V., 1889-91— and other papers. 



t Winogradsky, S. tlber Sohwefelbakterien. Botanische Zeitung, 1887. 

 Beitrage zur Morphologie u. Physiologic der Bakterien. Leipzig, 1888. 



