52 PHYSIOLOGY OF NUTRITION 



utilize hydrogen. 1 The former can derive its nourishment from organic com- 

 pounds but it can also grow in purely inorganic media, in which case it 

 assimilates carbon dioxide and hydrogen from the atmosphere and forms for- 

 maldehyde according to the equation, H 2 C0 3 + 2H2 = CH 2 + 2H2O. 

 Niklevskii 2 has isolated two bacteria {Hydrogenomonas nitrea and H. flava) 

 that can live upon an inorganic substratum with an atmosphere of hydrogen 

 and oxygen containing some carbon dioxide. They form organic compounds 

 from hydrogen and carbon dioxide, which are then oxidized to carbon dioxide 

 and water during respiration. The assimilation of hydrogen ceases when they 

 are grown upon organic substances. 



In all cases here described, of nutrition of bacteria by inorganic substances, 

 the production of organic compounds occurs without the agency of sunlight. 

 The formation of hydrogen, hydrogen sulphide and ammonia (by reduction of 

 oxidized compounds existing in nature, such as water, sulphuric acid and 

 nitric acid), goes on at the expense of radiant energy assimilated in green leaves, 

 however. Therefore it is indirectly at the expense of this energy that nitrifying 

 bacteria, sulphur bacteria and hydrogen bacteria are able to exist. 6 



1 Methane (CH4) which is frequently given off during the putrefaction of organic substances, can also 

 serve as a nutrient material for some bacteria. [See: Sohngen, N. L., Ueber Bakterien, welche Methan 

 als Kohlenstoffnahrung und Energiequelle gebrauchen. Centralbl. Bakt. II, 15 : 513-517. 1906.] 



2 Niklewski, Bronislaw, Ueber die Wasserstoffoxydation durch Mikroorganismen. Jahrb. wiss. Bot. 

 47: 113-142. 1910. 



6 In the foregoing discussion the terms "combustible" or " oxidizable " and "non-combus- 

 tible" or " non-oxidizable " substances should be considered as synonymous with the more ac- 

 curate ones "substances of high energy content" and "substances of low energy content." 

 Although plant physiology has never yet received adequate treatment from the standpoint of 

 energy transformations, some of the more general principles of such a treatment are well recog- 

 nized and are pertinent in the present connection. Energy can no more be destroyed or 

 created than can matter, so that when compounds of high energy content (carbohydrates, 

 proteins, etc.) are formed from compounds of lower energy content (carbon dioxide, water, 

 inorganic salts, etc.) energy must be supplied from some source other than the reacting mole- 

 cules themselves. Since the reverse process yields energy it is conceivable that some of the 

 energy obtained by the oxidation of large organic molecules may enter into reaction by which 

 other complex compounds may be formed. This appears to take place to some extent in 

 green plants, in the formation of proteins, cellulose, etc., and in parasites and saprophytes. It 

 is also conceivable that other substances that yield energy upon oxidation may enter into 

 analogous reactions. That this possibility is realized in the cases of some bacteria seems to be 

 true, and is one of the chief contributions that the investigation of these forms has made to 

 general physiology. Beggiatoa, which the author mentions, appears to be able to form 

 complex organic molecules from carbonates by means of the energy derived from the oxida- 

 tion of hydrogen sulphide. (See: Keil, Friedrich, Beitrage zur Physiologie der farblosen 

 Schwefelbakterien. Cohn's Beitrage zur Biol. d. Pnanzen 2: 335-372. 1912.) 



Bacteria that produce hydrogen sulphide must derive the necessary energy from other reac- 

 tions that yield energy, as from the oxidation of carbohydrates. Many other colorless bacteria 

 are similar in this respect. Besides the authors already cited in the text, see: Keil, 1912 (just 

 cited). Hinze, G., Thiophysa volutans, ein neues Schwefelbakterium. Ber. Deutsch. Bot., Ges. 

 21 : 309-316. 1903. Molisch, Hans, Neue farblose Schwefelbakterien. Centralbl. Bakt. 

 II- 33' 55 - 62. 191 2. Lauterborn, Robert, Eine neue Gattung der Schwefelbakterien 

 (Thyoploca schmidlei, nov. gen., nov. spec). Ber. Deutsch. Bot. Ges. 25: 238-242. 1907. 



Other bacteria oxidize sulphites, the liberated energy apparently enabling them to form 

 complex carbon compounds from mineral carbonates and bicarbonates. (See Nathansohn, 



