46 



PHYSIOLOGY OF NUTRITION 



nitrifying bacteria only, by preparing a nutrient solution containing no organic 

 substances. This nutrient mediumi contained i g. of ammonium sulphate and 

 I g. of potassium phosphate, dissolved in a liter of water. From 0.5 to i.o g. 

 of basic magnesium carbonate was added to each 100 cc. of this solution. 

 Nitrifying bacteria were able to develop excellently in this medium; they 

 oxidized ammonia to nitric acid and formed an appreciable quantity of organic 

 substance, thus assimilating the carbon dioxide of the air without the agency 

 of sunlight. Bacteria that need organic substances for their nutrition could 

 not develop in such a medium. 



Pig. 29. — Hydnora africana. t, part of the underground stem of the host plant; bl, one of 

 the mature fiowers; bl', bl", flower buds of the parasite. (J^ natural size.) {After Sachs.) 



Without the agency of sunlight as source of energy green plants are unable to 

 produce organic substance from the inorganic materials that serve as nutrients 

 for these forms. As has been said, there are other inorganic substances, 

 however (such as ammonia and hydrogen sulphide) that can serve as sources of 

 energy for such plants as the bacteria just mentioned. These substances are 

 common in nature, being frequently of organic origin as decomposition products 

 of complex organic compounds, and, although they do not contain carbon 



' IWinogradsky, S., Recherches sur les organismes de la nitrification. I. Ann. Inst. Pasteur 4 : 213-331. 

 1890. Idem, same title, II. Ibid. 4: 257-27S. 1890. Idem, same title, III. Ibid. 4: 760-771, 1890). 

 Idem, same title, IV. Ihid. 5: 52-100. 1891. [Idem, same title, V. Ibid. 5: 577-616. 1891. See No.' 

 IV. especially.] 



