PHYSIOLOGY OF THE SULPHUR BACTERIA. 371 



greater or lesser degree of vigour. It depends, therefore, on 

 external conditions, and consequently cannot be relied on as 

 was done previously by various observers : inter alia, Winter in 

 Rabenhorst's "Kryptogamen Flora" and by Engler as a character- 

 istic for the differentiation of species. The sulphur does not 

 permanently remain in the cells, but is oxidised by them to 

 sulphuric acid, the latter being then absorbed by the carbonates 

 usually CaH 2 (C0 3 ) 2 in the water, and converted into sulphates. 



If these Schizomycetes are deprived of sulphuretted hydrogen 

 for a long time, they consume their internal store of sulphur 

 (which will be exhausted in twenty-four to forty-eight hours), 

 and then perish of hunger. This fact demonstrates that the 

 sulphur bacteria cannot permanently dispense with sulphuretted 

 hydrogen, but that this gas is actually their special (and almost 

 exclusive) source of energy. Sulphur, or rather its compound 

 with hydrogen, plays the same part towards these organisms as 

 the carbohydrates do towards the majority of Schizomycetes ; its 

 combustion liberates the energy necessary to the maintenance of 

 their vitality. According to the observations of Winogradsky, 

 the individual threads of Beggiatoa daily consume from two to 

 four times their OAvn weight of the gas. These Schizomycetes 

 require but little other (organic) nutriment, and in fact will not 

 stand very much. This explains, on the one hand, their unusu- 

 ally slow rate of growth in proportion to the amount of sulphur 

 separated, and, on the other, their inability to grow in the ordinary 

 nutrient media employed in bacteriology : e.g. on gelatin they 

 perish in a very few minutes. Attempts to grow them as pure 

 cultures on a large scale have hitherto failed, and the physiological 

 facts determined concerning them have all had to be ascertained 

 very laboriously by cultivating single organisms in sulphur-water 

 on microscope slides. 



The optimum, i.e. the maximum supportable, quantity of sul- 

 phuretted hydrogen in the water is higher in the case of the red 

 sulphur bacteria than with the colourless, filamentous species. 

 These latter require less, and in fact die instantly if placed in 

 water saturated with the gas, whereas the red kinds will stand this 

 degree of concentration very well. Consequently, under natural 

 conditions, these latter will gain the upper hand in such places 

 where large quantities of sulphuretted hydrogen are evolved, either 

 as a result of the decomposition of an abundance of organic 

 matters (albumin) or by the powerful reduction of sulphates. 

 This is the case, for example, in the stagnant shallow bays on the 

 Danish Zeeland coast, and the same conditions obtain in the 

 Limanes so plentiful along the coast of the Black Sea (e.g. near 

 Odessa). These latter are shallow salt lakes, separated from the 

 open sea merely by a low, narrow tongue of land. Their bottom 

 is covered by a thick mud, which owes its black colour to the FeS 

 thrown down from the iron compounds in the water (and in the 



