8o ORGANIC FUNCTIONING 



acid, nitrous acid into ammonia, and ammonia into elementary 

 nitrogen (the denitrifying bacteria), or they can use the elementary 

 nitrogen of the atmosphere (nitrogen-fixing bacteria). Some 

 species can use CO 2 and OH 2, synthesizing these into carbo- 

 hydrate with only a trace of organic matter and in the dark. 



(b) Sulphur and Iron Bacteria can use sulphuretted hydrogen 

 and iron salts as the raw materials for assimilation. Possibly 

 there are analogous carbon and silica bacteria. 



(c) The Root- Bacteria of Leguminous Plants. These are 

 symbiotic with the tissues of the roots of peas, beans, etc. They 

 can use elementary nitrogen. 



(it) The myxotrophic forms. 

 These are all the ordinary bacteria that may live in the open, 

 or in organic matter, or in the tissues of animals. They are 

 responsible for the processes of putrefaction and fermentation of 

 organic materials. They get their energy by breaking up such 

 substances. 



(m) The paratrophic forms. 

 These are the obligatory parasites and they occur only in the 

 tissues and fluids of living organisms. These fluids and tissues 

 are their raw food substances. 



28. ON THE PRELIMINARY TRANSFORMATIONS OF THE 



INTAKEN MATERIALS 



First we consider briefly the typical plant modes (see also 

 Section 35). 



zSa. Photosynthesis of Carbohydrates and Proteins. 

 CO 2 is taken into the plant tissues ma the stomata of the green 

 surfaces (leaves) and water containing inorganic nitrogenous and 

 other salts is taken in via the roots and is transported to the tissues 

 adjacent to the green surfaces. Here the CO 2 and OH 2, plus 

 the energy of sunlight, combine to form sugar-like materials which, 

 almost immediately, become further chemically transformed and 

 are deposited in the leaf- tissues as sugar and starch granules. 



At the same time simple proteins are synthesized from the sugar 

 thus formed and the nitrogenous materials which were absorbed 

 via the roots. These also are, at first, stored. This, in the 

 case of starch formation, is carbon-assimilation. In the bacteria 

 there are analogous processes of sulphur — and iron — assimilation. 



