276 LIFE : OUTLINES OF GENERAL BIOLOGY 



SOME STRANGE BACTERIA.— In further illustration of nutritive 

 peculiarities it is interesting to refer to the strange life of some 

 Bacteria. To show these in proper relief, a slight recapitulation is 

 necessary. 



All living matter is made up of complex compounds of carbon, 

 and the energy of vital processes is derived from the chemical 

 breaking-dowTi of these complex substances into simpler ones. In 

 nearly all cases this breaking-down is accompanied by an uptake 

 of oxygen gas from the atmosphere, so that the final product is 

 carbon dioxide. In the same way, a candle takes oxygen from the 

 air and gives off carbon dioxide as it bums; but the complex sub- 

 stances of the candle are gradually used up; a burning candle has 

 a short life. Animals, on the other hand, constantly replace the 

 carbon compounds as they are consumed ; the food materials taken 

 into the body make good the loss. It follows that animals, and 

 some simple plants, depend on a food supply of suitable carbon 

 compounds; without this they starve and die. The green plants, on 

 the contrary, are not dependent on a food supply of carbon com- 

 pounds; they entrap the energy of the sunlight, and with this 

 energy build complex substances from the simple carbon dioxide 

 they draw from the air. In the dark, deprived of the energy 

 of light-rays, they are unable to do this. This is all familiar 

 ground. 



There are a few strange bacteria which build up carbon dioxide 

 into complex compounds, even in the dark. The energy required for 

 the formation of the complex substances is drawn not from light 

 but from chemical reactions of varied and peculiar types. 



One of these Bacteria, Beggiatoa by name, lives in natural 

 mineral waters which contain that evil-smelling gas, sulphuretted 

 hydrogen. From this compound the Beggiatoa forms ordinary 

 yellow sulphur, of which the living cells show abundant granules. 

 The sulphur is then combined with oxygen from the air to form 

 sulphuric acid. From these reactions the bacterium derives enough 

 energy to build carbon dioxide into the complex substances of 

 which its living matter is composed. 



Other bacteria solve the same problem in analogous ways, but 

 make use of different energy-yielding chemical reactions. Some 

 combine oxygen with iron, and become so clogged with rusty 

 particles that they block up water-pipes and give endless trouble 

 to engineers. Some combine hydrogen with oxygen to form water, 

 and derive much energy from this! A large and important group 

 carry out various reactions with nitrogen and its compounds, and 

 play an indispensable part in preventing soils from becoming 

 exhausted and useless for plant growth. How clearly these many 

 solutions to one problem illustrate the adaptability of living 

 organisms ! 



