RESPIRATION AT THE EXPENSE OF MINERAL SUBSTANCES I51 



We are entirely justified in calling this process respiration, 

 especially since no simultaneous combustion of organic sub- 

 stance takes place in these forms. According to the work of 

 Meyerhof,^ the amount of atmospheric oxygen absorbed by 

 Nitrohacter corresponds exactly to the amount of nitrite oxi- 

 dised: hence an oxidation of organic substance is precluded. 

 This is apparent from the following table : 



O2 Used to Oxidise 

 O2 Absorbed the Nitrite 



o. 270 cc. o. 273 cc. 



0.392 cc. 0-396 cc. 



c. 277 cc. o. 290 cc. 



o. 293 cc. o. 295 cc. 



o. 244 cc. o. 240 cc. 



From this we understand how Nitrohacter obtains the energy 

 for its vital processes in the absence of organic substances. 

 The oxidation of NH3 or HNO2 is so vigorous that, as is well- 

 known, the free energy suffices to assimilate the atmospheric 

 carbon dioxide without the intervention of radiant energy. 

 For Nitrosomonas Winogradski found that one atom of carbon 

 is assimilated for each 33.3-36.6 molecules of oxidised ammonia. 

 According to Meyerhof, Nitrohacter assimilates one atom of 

 carbon for each 131-146 molecules of oxidised nitrite. The 

 figures correspond exactly to the heat release from the oxidation 

 of ammonia and nitrite. 



2. SULPHUR BACTERIA, IRON BACTERIA, HYDROGEN BAC- 

 TERIA, ETC. 



The peculiar behavior of the sulphur bacteria, first described 

 by Winogradski,- means that here there is likewise a respiration 

 at the expense of mineral substances. It was shown by the 

 studies of Dangeard and KeiP that Beggiatoa can be grown in 

 pure cultures on purely mineral solutions. Under these con- 

 ditions Beggiatoa assimilates the carbon dioxide of the air and 

 so its behavior is entirely analogous to that of the nitrifying 



1 Meyerhof, O. Arch. ges. Physiol. 164: 353- 1916. 



2 Winogradski, S. Bot. Zeitschr. 45: 489- 1887; Ann. de I'inst. Pasteur. 3: 49. 1889. 

 [Baas-Becking (Ann. of Bot. 39: 613-650. 1925) has recently given a complete statement 

 of the physiology of this group of bacteria.] 



2 Dangeard. Compt. rend. 153 : 963. i9ii;Keil. Cohns Beitr. 11 : 335. 1912. 



