No. 414.] NORMAL RESPIRATION. 467 
simpler nitrogen compounds in order to liberate energy, employ- 
ing carbon compounds only in the synthesis of food to be 
used in the construction of their own bodies. One set of 
nitro-bacteria oxidize ammonia, or compounds of ammonia, to 
nitrous acid, the first and last steps of the process being thus 
indicated : 
2NH,0H T 302 = 2 HNO, + 4 H20. 
Another set oxidize the nitrous acid, or its salts, to nitric acid, 
thus : 
2 HNO, + Os = 2 HNO, 
The sulphur bacteria (Beggiatoa, Chromatium, etc.) obtain 
most if nót all of their kinetic energy by oxidizing sulphur 
compounds. They precipitate sulphur in their own bodies by 
oxidizing the sulphureted hydrogen present in the water in 
which they live.! If the supply of gas remain sufficient, 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: 
| 2 H,S + 0, 2 2 H0 +S 
S +0, = $0; 
2 SO: + O: = 2 $0, 
SO; + H,O = H5;SO, 
Those bacteria (z.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 oxidizing 
ferrous compounds, presumably ferrous oxide, to ferric oxide.? 
Other bacteria may be discovered which, needing carbon and 
nitrogen compounds only to supply the constructive elements 
of protoplasm, obtain their needed energy by oxidizing other 
substances present in solution in the waters in which they live. 
: Winogradsky, S. Ueber Schwefelbakterien, Botan. Zeitung, 1887. Beiträge 
zur Morph. u. Physiol. der Bakterien. Leipzig, 1888. Miyoshi, M. Studien über 
de Schwefelrasen-Bildung und die Schwefelbakterien der Thermen von Gumoto 
bei Nikko, Journ. Coll. Sci. Imp. Univ. Tokyo, Bd. x, pt. ii, 1897. 
* Winogradsky, S. Ueber Eiseribakterien, Botan. Zeitung, 1888.  Molisch, H. 
Pflanze in ihren Beziehungen zum Eisen. Jena, 1892. Miyoshi, M. Ueber ' 
massenhafte Vorkommen von Eisenbakterien in den Thermen von Ikao, 
Journ. Coll. Sci. Imp. Univ. Tokyo, pt. ii, 1897. 
