6 Biological Relation Between Bacteria and the More 



tissues and special organs. Their food supply consists of 

 dissolved or soluble salts of various kinds in the soil and 

 water, and of the carbonic acid of the atmosphere. 



On the other hand, the bacteria and other chlorophyl- 

 free plants subsist mainly upon nitrogenous organic mat- 

 ter or upon inorganic compounds containing nitrogen, 

 such as the various salts of ammonia and the nitrates, from 

 which they derive their supply of nitrogen. In most in- 

 stances the nitrogen is most readily taken from diffusible 

 albuminoid matter; less easily from the ammonia com- 

 binations. 



Nageli was able to demonstrate that a certain class of 

 bacteria known as the denitrifying bacteria were able to 

 bring about the reduction of nitrates and convert them 

 into nitrites, ammonia, or even nitrogen. 



A quite exceptional mode of meeting the demand for 

 nitrogen is found in those bacteria forming the tubercles 

 on the leguminoseae and allied plants in which they, in 

 symbiosis with the host plants on which they live, are 

 capable of fixing the free nitrogen of the atmosphere and 

 assimilating the same in building up their cell bodies. 



The supply of carbon of the chlorophyl-free plants, in 

 contradistinction to that of the higher plants, is obtained 

 by breaking up different forms of carbo-hydrates. Aside 

 from albumen and peptone, they use sugar and similar 

 carbo-hydrates and glycerine, as a source of carbon. They 

 are also capable of using organic matters of different chem- 

 ical constitution, as the basic and diabasic acids (vinegar), 

 the hydroxilized acids (tartaric and citric), as asparagin, 

 lucin, the different alcohols, amine, ester, urea, etc. In 

 very dilute solutions they are even capable of using as 

 nourishment compounds containing carbon which, in con- 

 centrated solutions, are distinctly poisonous, such as car- 

 bolic acid and salicylic acid. 



Some of the chlorophyl-bearing organisms, such as the 

 algae, which closely resemble the bacteria in some respects, 



