SULPHUR BACTERIA 65 



at fault, since it affords nourishment only to mctatrophic forms, not to 

 prototrophic, and it is just these latter that we might expect to find on 

 the ocean floor. It is not at all unlikely that there are species characterized 

 by an extremely simple type of metabolism, which would throw new light 

 upon the mysteries of marine life. Russel has discovered aerobic bacteria 

 that reduce nitrates in samples of mud from the sea-bottom. 



In the aerobic bacteria which we have been considering, respiration 

 consists essentially in the oxidation of complex organic substances, the 

 energy thus set free being necessary for the processes of life. In the case 

 of the anaerobes the energy developed, although smaller in amount, is 

 likewise derived from the splitting-up of fermentable and putrescible organic 

 substances. Both classes, aerobes and anaerobes, are metatrophic in this 

 respect. There is, however, in certain prototrophic bacteria a process going 

 on comparable to respiration, but consisting in the oxidation of inorganic 

 compounds. The micro-organisms in question arc the nitre bacteria 

 (see p. 105) and the remarkable 

 sulphur bacteria, the classical 

 examples of prototrophic re- 

 spiration. 



The sulphur bacteria (36), 

 Tliiobacteria (p. 13), whose 

 cells are often crammed full of 

 spherical refringent masses of 

 pure sulphur, occur in nature 

 in places where free sulphur- 

 etted hydrogen is present. 

 Such are sulphur springs where 

 the SH., is principally of mineral 

 origin, and the mud of standing 



waters and of the sea-bottom, where it is set free by the putrefaction of dead 

 plants and animals *. The bacteria were formerly thought to produce the 

 SH.,, and therefore to play an important part in the origination of sulphur 

 springs, but the splendid researches of Winogradsky have shown that the 

 micro-organisms need the gas as a food-stuff, and are unable to live without 

 it. Thiobacteria can be found at any time of the year, but are most 

 abundant in the early spring and late autumn, periods when the remains 

 of the summer's vegetation in standing waters are plentiful, and when the 

 putrefactive processes set up by other bacteria cause an evolution of SH 2 . 

 The sulphur bacteria frequently form a snow-white furry coat on the rotting 

 vegetation, with here and there pink or pale puce-coloured patches. 



FlG. 17. Sulphur Bacteria, a-c, Bezgiatoa. a full of sulphur 

 (black rings) ; 6, partly <le prived of sulphur by lying 24 hrs. in 

 spring water ; c, almost free from sulphur after another day or 

 two in pure water, rf, Chromatittm Okenii, dirty pink erythro- 

 bacterium ; e, piece of a mesh like zoogloea of Lamprocystis 

 roseo-fiersicina. Magn. a-c 1000, d you, e 500. a-c from Wino- 

 gradsky, d, e from Zopf. 



* The ' dead-ground ' of the Bay of Kiel and the ' Limanes ' of the Black Sea are instances. 



FISCHER F 



