370 THE SULPHUR BACTERIA. 



202. Physiology of the Sulphur Bacteria. 



The true nature of the rounded, highly refractive enclosures 

 present in these fission fungi, and attracting the eye of the micro- 

 scopist, was first recognised by Cramer, whose discoveries are 

 noticed in a treatise by C. MULLER (I.). It was shown in these 

 experiments that these granules behaved exactly like sulphur in 

 presence of solvents, and they were therefore thought to consist of 

 that element. F. COHN'S (II.) extension of these investigations 

 (which were confined to Beggiatoa, and were confirmed by J, 

 Mayer-Ahrens) to the red sulphur bacteria as well, led to the- 

 same result : the granules appearing in these coloured Schizo- 

 mycetes, under certain as yet undefined conditions, are com- 

 posed of pure sulphur. The term granules applied to these forms 

 is unsuitable, inasmuch as they consist not of solid granular, but 

 (as Winogradsky afterwards proved) of oily, amorphous sulphur, 

 the greater part of which is soluble in CS 2 . However, when the 

 enveloping cells are killed, the sulphur granules are gradually 

 changed into the crystalline modification of this element. If a 

 few Beggiatoa threads rich in these droplets be immersed in 

 concentrated picric acid and left in water, a number of very fine 

 monoclinic prismatic plates and rhombic octahedra will be found 

 in the threads after a lapse of twenty-four hours, and it will at 

 the same time be noticeable that the growing crystals have pene- 

 trated the adjacent cell walls. 



F. Cohn was the first to investigate the origin of these internal 

 constituents, which occasionally fill the cell to such an extent as 

 to exceed 90 per cent, of its weight. Starting from the fact that 

 the sulphur bacteria are only found in abundance in natural waters 

 containing sulphuretted hydrogen, and are, on the other hand, 

 almost entirely lacking elsewhere in Nature, he came to the 

 opinion that this gas is produced by the reducing action of these 

 fission fungi on the sulphates in the water, and that they subse- 

 quently reoxidise the gas, sulphur being then left as a deposit in 

 the cells. In forming this opinion he was chiefly influenced by 

 the result of an investigation made by LOTHAR MEYER (L), who 

 kept a sample of sulphur-spring water (rich in Beggiatoa} from 

 Landeck in Silesia for four months in a stoppered flask, and found 

 that at the end of that time it contained five times as much H 2 S 

 as at first. The same conclusion as deduced by Cohn was also 

 arrived at by E. PLATJCHU (I.), and by A. ETARD and L. OLIVIER 

 (L). This hypothesis, which credited the sulphur bacteria with 

 both a reducing and an oxidising capacity, was first thoroughly 

 investigated in 1886 by S. WINOGRADSKY (VI.), who showed that 

 the sulphur bacteria consume (instead of producing) sulphuretted 

 hydrogen ; oxidising it and storing up the separated sulphur in 

 their cells. The amount of these enclosures in the cell is larger 

 or smaller according as this process can be carried on with a 



