286 THE SULPHUR BACTERIA 



shown (enlarged) in Fig. 80. The examination of these tufts by the aid of 

 a horizontal microscope shows that they are formed by the movement of the 

 individual bacteria, in a manner similar to the gushing of a spring ; they ascend 

 in the axis of the tuft, and then describe an arc in their return to the plane. 

 When inverted by the microscope this resemblance is still more striking ; so 

 that Jegunow has styled the planes " fountain planes." The velocity of the 

 individual cells he found to be 0.02 mm. per second. In tracing the chemical 

 activity of the bacteria, he made use of a simple and reliable reagent for sulphu- 

 retted hydrogen : a fine (woollen or similar) thread treated first with ferric 



FIG. 80. A portion of the Bacterial plane from the preceding Fig. 

 showing the arched construction of the plane itself, as well as 

 four of its fountains. Magn. n. (After Jegunow.) 



FIG. 79. Culture of Sulphur Bacteria from the Limanes (in a small vessel ; reduced scale). 



The figures on the label give the dimensions, the thickness of the layer of liquid being 0.9 mm. The 

 bottom is occupied with black Limanes mud; above this is the liquid, the meuiscus'of which is 

 visible at the top of the Fig. ; and in between is the bacterial plane with five " fountains." (After 

 Jegunow. ) 



chloride and then with ammonia, both in such a very dilute condition that the 

 thread is stained merely a pale yellow. A glass weight is then attached to the 

 thread and let down into the liquid, whereupon the lower part of the thread, as 

 far as the summit of the tufts on the fountain plane, quickly turns black, from 

 the formation of FeS. From that point onwards, however, the colour gradually 

 changes to white. This experiment shows that in the summits of the tufts the 

 sulphuretted hydrogen arising from below is first oxidised to sulphur, and stored 

 up in the cell, which conveys it to a higher level (the actual plane), and there 

 oxidises it to sulphuric acid. This acid then dissolves the ferric oxide on the 

 upper part of the thread, which is consequently decolorised at this level. The 

 time occupied by the cells in making a single trip and therefore the total 



