SULPHUR AND NITROGEN BACTERIA 223 



autotrophic ; it has always been considered as a heterotrophic form. In 

 WINOGRADSKY'S micro-cultures in which vigorous increase took place, the 

 Langenbriicken mineral water was the only nutrient supplied, and that fluid 

 contains nitrogen only as traces of ammonia and nitric acid, and only 0-0005 per 

 cent, of organic materials, i. e. in infinitesimal quantity. These are sufficient, as 

 we have seen, to support both life and growth, although they are qualitatively 

 not of a kind one would reckon as of nutritive value. According to FRESENIUS'S 

 investigations, the nutrients must, in part at least, consist of formic and pro- 

 pionic acids. When WINOGRADSKY employed solutions containing sugar, 

 peptone, asparagin, &c., he was unable to obtain as good cultures of Beggiatoa 

 as in Langenbriicken water, indeed, for the most part, the plants rapidly 

 succumbed to such treatment. 



The general conclusion which WINOGRADSKY arrived at, as based on his 

 experiments on Beggiatoa, is as follows : The oxidation of sulphuretted 

 hydrogen to sulphuric acid is a process in the course of which energy is set 

 free, and in Beggiatoa this energy takes the place of that released normally in 

 respiration. While ordinary organisms must devote organic substance, or 

 even part of their own bodies to respiratory purposes, Beggiatoa respires sul- 

 phuretted hydrogen, and thus saves its organic constituents. It is thus con- 

 ceivable that it makes such moderate demands on nutrients, both in quality 

 and quantity, that it employs these only for constructing its body and not 

 as a means of supporting vital processes (p. 229). WINOGRADSKY does 

 not deny the possibility of the existence of a normal respiration taking place 

 in addition to the oxidation of sulphuretted hydrogen, but he does not consider 

 it probable. 



To Beggiatoa are related on the one hand the colourless sulphur-bacteria 

 (species of Thiothrix), which are precisely like it in all essentials (though WILLE, 

 1902, Biolog. Centrbl. 22, 257, has recently denied the occurrence of sulphur 

 in Thiothrix ; compare MOLISCH, 1903, Bot. Ztg. 61, 57), on the other hand, 

 there is a large number of so-called red sulphur-bacteria (Fig. 39, d, e) which 

 physiological research has shown to exhibit important differences from Beg- 

 giatoa, although no satisfactory conclusions have as yet been reached with 

 regard to them. They are distinguished in the first place by possessing a red 

 colouring matter (bacterio-purpurin) of varying tint, but its characters so 

 far as they are known afford no indication of its physiological significance. 

 These Bacteria are further distinguished from Beggiatoa by their mode of 

 occurrence, since they prefer water containing large amounts of sulphuretted 

 hydrogen, and are not injured even when that compound is present in a con- 

 centrated condition. They are, apparently at least, anaerobic, and avoid 

 situations where oxygen is abundant. Finally, they prefer light to darkness 

 and move towards it, whilst Beggiatoa avoids light. In common with the 

 latter they make use of sulphuretted hydrogen. Since they live in concen- 

 trated solutions of this gas, the question as to how they are able to obtain the 

 necessary oxygen must not be overlooked. According to WINOGRADSKY 

 (1888, b), they always live in association with other micro-organisms which are 

 provided with chlorophyll, and which therefore can decompose carbon-dioxide 

 and give off oxygen. The red sulphur-bacteria then absorb the traces of 

 oxygen present, and use it for oxidizing sulphuretted hydrogen. WINO- 

 GRADSKY, in fact, was able to cultivate red sulphur-bacteria only when he 

 associated them with green forms of this kind. 



ENGELMANN (1888) offers another explanation of this phenomenon. He 

 has proved by means of the bacterium method previously described (p. 105) 

 that the red sulphur-bacteria decompose carbon-dioxide with the aid of light, 

 and especially of the ultra-red rays, and employ the oxygen so obtained in 

 oxidizing sulphuretted hydrogen. This view of the phenomenon may be 

 preferable, inasmuch as it gives a special function to the presence of bacterio- 



