106 BACTERIOLOGY. 



H.COOH + H 2 = CHOH + H 2 O 

 formic acid, hydrogen, formaldehyde, water. 



IIO.COH + H 2 = H.COH + H 2 

 formic acid, formaldehyde. 



From formaldehyde upwards is consummated 

 the synthesis of the carbohydrates, those sub- 

 stances devoid of nitrogen which are an im- 

 portant constituent of proteid and are funda- 

 mentally alike in green plants and in organ- 

 isms which lack chlorophyl. 



From the foregoing statements it might be 

 taken for granted that formaldehyde marks 

 the lowest limit at which chlorophyl-lacking 

 organisms are able to begin the construction 

 of organic substance, and that nothing but the 

 presence of leaf-green or chlorophyl qualifies 

 an organism for the assimilation of carbonic 

 acid in combination with ammonia. But this 

 limit does not exist. One of my pupils, 

 Heraeus, made the observation, the signifi- 

 cance of which he did not at first grasp, that 

 even bacteria devoid of pigment can at times 

 nourish themselves with ammonium carbonate. 

 This power, I found, occurs only among the 

 nitrifying microbes, which are able to oxidize 

 ammonia to nitrous and nitric acid. I ascer- 

 tained further that it is this combustion of 

 ammonia that furnishes the energy for the 

 synthesis and assimilation of carbonic acid and 



