52 FROM DUST TO DUST. 



which has been stored up, within the seed itself, by the mother 

 plant. These nitrifying bacteria, on the contrary, seem to thrive 

 best in a medium devoid of all organic matter ; and this is of the 

 greatest importance in the economy of Nature. Prof. Frankland* 

 has kept them alive for four years in a purely mineral solution ; 

 and Winogradsky proved that they not only flourish, but multiply 

 and build up living protoplasm, in a solution from which organic 

 matter has been rigorously excluded. Other bacteria transform 

 iron and iron-peroxide into oxide of iron ; whilst others oxidise 

 sulphuretted-hydrogen, and transform it into sulphur and sulphuric 

 acid, but as these are inimical to vegetable and animal life we 

 need not speak further of them. 



Prof. Stoney asks : — t" Whence comes the vital energy of the 

 innumerable bacilli which are excluded from the direct influence 

 of sunlight, and why are these organisms all extremely minute ? " 

 There are some bacilli {e.g.^ the nitrifying bacilli of the soil) which 

 seem to thrive entirely upon mineral food, and not only so, but 

 perform their functions while completely removed from the sun's 

 rays. The manufacture of protoplasm and other complex com- 

 pounds from inorganic matter involves a considerable amount of 

 energy, and the bacilli must somehow obtain this from the sur- 

 rounding gases and liquids; Prof. Stoney regards it as conceivable 

 that the energy may be imparted to the organisms directly by the 

 impact of the more swiftly moving molecules of these gases and 

 liquids ; and if that be the case, then the necessity for the exces- 

 sive minuteness of the bacilli — scarcely more than molecules — 

 is explained. 



Nitrogen is quite as necessary for plant-life as for that of the 

 animal. It exists in the soil, even when it is not manured, and 

 largely, as we know, in the atmosphere. It is only recently, how- 

 ever, that we have any certain knowledge of the means whereby 

 the free nitrogen of inorganic nature becomes part of a living 

 body. That plants do not obtain their nitrogen from the air by 

 the action of their leaves has been conclusively proved, and it has 

 now been clearly established that those which are not insectivorous 



* Prof. Percy Frankland, Our Secret Friends and Foes, p. Z^. 



t Sci. Proc. Roy. Dublin Soc, n.s., v. viii., pp. 154, 156, quoted in 

 Natural Science, v. iii., p. 252. 



