SULPHUR AND NITROGEN BACTERIA 221 



organism, and detailed research confirms this view. For long Beggiatoa was 

 believed to be the cause of the formation of sulphuretted hydrogen, until Hoppe- 

 SEYLER (1886) proved that this was not the case, but that Beggiatoa gave rise 

 to sulphur by oxidizing sulphuretted hydrogen (H^S + O = HjO + S). More 

 recently Winogradsky (1887), in a classical monograph, traced out the pro- 

 cess in an exhaustive manner, and showed what its significance was in the 

 economy of the organism. [Omelianski (1904) has also provided us with 

 a comprehensive exposition of the physiology of the sulphur-Bacteria.] 



Beggiatoa occurs in nature in the mud associated with salt or fresh water, 

 wherever the water or mud contains a sufficient quantity of sulphates. The 

 part these sulphates play, however, is only to supply the material from which 

 other organisms may develop sulphuretted hydrogen. When sulphuretted 

 hydrogen is itself present in the water sulphates are quite superfluous. Beggiatoa 

 then appears in the sulphur-containing medium, and develops in it luxuriantly. 

 Winogradsky proved that Beggiatoa was present in ever decreasing numbers 

 when the source of sulphur was gradually diminished, and that when the sul- 

 phuretted hydrogen was completely absent from the water, Beggiatoa also 

 disappeared. 



These observations of natural conditions teach us how important sul- 

 phuretted hydrogen is for the maintenance of the life of Beggiatoa, but con- 

 vincing evidence and a more exact knowledge of this phenomenon are to be 

 obtained by cultures. If we attempt to cultivate Beggiatoa by the methods 

 employed for the majority of Fungi and Bacteria, presenting it with a solid 

 or fluid substratum rich in organic material, it dies off in a very short time. 

 If, on the other hand, we place a small quantity of Beggiatoa on a slide, cover 

 it, and keep supplying it daily with fresh quantities of water containing sul- 

 phuretted hydrogen (Winogradsky used natural water obtained from the 

 Langenbriicken Baths, to which more sulphuretted hydrogen was added), it not 

 only remains alive, but increases so rapidly that large quantities have to be 

 removed in order to make room for the development of what is left. With the 

 aid of such a micro-culture in a healthy state of growth we are able to carry 

 out easily the following decisive experiments : — 



1. The culture is treated twice daily with Langenbriicken sulphur-water, 

 which has been deprived of its sulphuretted hydrogen by being exposed to 

 air. The Beggiatoa soon loses its sulphur, and is unable to form more ; it 

 then gradually dies off. 



2. If the culture, on the other hand, be supplied with the same water 

 containing sulphuretted hydrogen, Beggiatoa again develops rapidly. 



The only difference between the two cultures is the absence in one of 

 them of sulphuretted hydrogen, and hence it follows that this substance is 

 essential to Beggiatoa, and that from it Beggiatoa manufactures the sulphur 

 found among the cell contents. Since this is possible only by oxidation, 

 Beggiatoa is absolutely dependent on the presence of oxygen, although it 

 requires this element in quite definite quantities ; too little of it is as dis- 

 advantageous as too much. If the experimenter desires to regulate the amount 

 of oxygen supplied to the culture he will meet with insurmountable difficulties, 

 which at once disappear if the organism itself be allowed to regulate its own 

 supply of oxygen. Since Beggiatoa is a free motile form, it is able, just like 

 other motile organisms (p. 215) to find for itself the optimum concentration 

 of oxygen, provided all possible variations in oxygen tension occur between 

 the edge of the cover-glass and the centre. If we allow a drop of dilute sul- 

 phuretted hydrogen-water, free from Beggiatoa, covered with a cover-glass to . 

 stand in a moist chamber, we see after a few hours that the formation of 

 particles of sulphur which takes place under the influence of air, is apparent 

 only for a distance of a millimetre from the edge of the cover-glass, while 

 the central region remains for long unoxidized, provided that, by fre- 



