124 THE STORY OF GERM LIFE. 



ucts of the gas manufacture. From the coal 

 also comes coal tar, the material from which such 

 a long series of valuable materials, as aniline 

 colours, carbolic acid, etc., is derived. The list of 

 products which we owe to coal is very long, and 

 the value of this material is hardly to be over- 

 rated. In the preparation of these ingredients 

 from coal bacteria do not play any part. Most 

 of them are derived by means of distillation. But 

 when asked for the agents which have given us 

 the coal of the coal beds, we shall find that here, 

 too, we owe a great debt to bacteria. 



Coal, as is well known, has come from the ac- 

 cumulation of the luxuriant vegetable growth of 

 the past geological ages. It has therefore been 

 directly furnished us by the vegetation of the 

 green plants of the past, and, in general, it repre- 

 sents so much carbonic dioxide which these 

 plants have extracted from the atmosphere. But 

 while the green plants have been the active 

 agents in producing this assimilation, bacteria 

 have played an important part in coal manufac- 

 ture in two different directions. The first ap- 

 pears to be in furnishing these plants with 

 nitrogen. Without a store of fixed nitrogen in 

 the soil these carboniferous plants could not have 

 grown. This matter has already been considered. 

 We have no very absolute knowledge as to the 

 agency of bacteria in furnishing nitrogen for this 

 vegetation in past ages, but there is every reason 

 to believe that in the past, as in the present, the 

 chief source of organic nitrogen has been from 

 the atmosphere and derived from the atmos- 

 phere through the agency of bacteria. In the 

 absence of any other known factor we may be 

 pretty safe in the assumption that bacteria played 



