68 



RESPIRATION OF BACTERIA 



RESPIRATION OR LIBERATION OF ENERGY. 



These two tables give, of course, only a general view of the broader 

 outlines of the processes. Real and apparent exceptions will occur to the 

 student, but they do not impair the validity of the schemes as a whole. 

 The green plants derive from the sun the enormous amount of energy 

 necessary for the formation of carbohydrates out of carbonic acid and water, 

 and set it free again in the process of respiration. The metatrophic bacteria 

 make use of highly combustible organic compounds which they oxidize at 

 once, and the sulphur bacteria are able at little cost to store up sulphur. 

 The oxidation of this sulphur represents a very abundant supply of energy, 

 a supply that is probably far more than sufficient to cover the wants of the 

 organism living under the conditions already described, and building up its 

 protoplasm from the minute traces of fatty acids and ammonia contained in 

 the water it lives in. The question therefore naturally suggests itself whether 

 the bacteria have not some other use for the surplus energy. We know that 

 the nitrifying bacteria are able, without sunlight, by means of the energy 

 they obtain from the oxidation of nitrogen, to seize and assimilate the C0 2 of 

 the atmosphere, and perhaps the Thiobacteria are able to do the same with 

 the much more abundant energy derived from the oxidation of sulphur. 

 Should this supposition turn out to be true, we should have in the colourless 

 sulphur bacteria a group transitional as regards their physiology between 

 the Erythrobacteria and bacteria of ordinary metatrophic habit (37). 



The Erythrobacteria or coloured sulphur bacteria are unique in possess- 

 ing the power of assimilating CO a in the presence of sunlight by means of 

 a special red colouring-matter (Bacteriopurpurin) which exercises a similar 

 function to that of the chlorophyll of green plants. Engelmann has shown 

 that the spectrum of Bacteriopurpurin is of a very peculiar character, 

 having in addition to an absorption band between B and C another 

 very broad one in the region of the invisible ultra-red, where the wave 

 length is from o-8 /* to 0-9 p. By the bacterial method he was able to 

 prove that oxygen was evolved in both these regions, showing that the 

 invisible heat rays are utilized for the assimilation of C0 2 just in the same 



