352 FIXATION OF FREE NITROGEN BY BACTERIA. 



need to be eliminated anl only their assumed stimulating action 

 allowed to operate. However, the wished-for decision may be 

 expected from the experimental solution of the previous question, 

 and attempts may therefore be made to ascertain whether the 

 nodule bacteria are of themselves capable of fixing free nitrogen. 

 On this point BEYERINCK (XVII.) has conducted researches in 

 nutrient solutions with pure cultures of Bacillus radicicola, and 

 in this manner ascertained that during a period of two months 

 an increase of 9-18 m. grins, of combined nitrogen occurred per 

 litre. Nevertheless he considers that this discovery leaves the 

 question still undecided, and consequently a repetition and exten- 

 sion of his researches in this direction is highly desirable. 



The exercise of the still imperfectly proved capacity of Bacillus 

 radicicola for fixing free nitrogen is opposed by a considerable 

 obstacle consisting in the difficult accessibility of the interior of the 

 nodule (the chief seat of this fission fungus) to the gas to be fixed. 

 A. B. FRANK (VIII.) has ascertained that the air passages (inter- 

 cellular spaces) of the nodules lead only as far as the cambium 

 layer, but not into the bacteroidal tissue ; consequently atmos- 

 pheric nitrogen cannot penetrate directly to this tissue. On this 

 point R. BOUQUET (I.) has expressed an opinion worthy of further 

 investigation. According to him, it is the water absorbed by the 

 roots and exhaled through the leaves which conducts and gives 

 up free nitrogen in solution to the root cells, where it is then 

 combined by the plasma. 



If, then, we must consider the question, whether the fixation 

 of free atmospheric nitrogen is effected within the nodules, to be 

 still imperfectly solved, it is, on the other hand, clearly proved 

 that such an operation goes on in (uncultivated) soil. This was 

 first observed by M. BERTHELOT (I.) in 1885, and he subsequently 

 proved that this phenomenon is not occasioned by exclusively 

 chemical affinity, but is due to the activity of micro-organisms. 

 Opinions on the nature of the organisms were at first divided. 

 TH. SCHLOESING, jun., and EM. LAURENT (I.) ascribed the fixation 

 of nitrogen to certain lower algae (Conferva, Oscillaria, Nitzschia), 

 and mosses (Bryum, Leptobnjum). Doubt was cast on this hypo- 

 thesis by A. GAUTIER and R. DROUIN (I.), and P. KOSSOWITSCH (IL) 

 disproved it so far as the algae are concerned by the aid of 

 pure cultures. BERTHELOT (II.) then showed that the activity 

 of fungi both Eumycetes (such as Aspergillus niger, Alternaria 

 tennis, &c.) and Scliizomycetes is in question. 



For more precise investigations on this matter we have to 

 thank S. WINOGRADSKY (II.), who described a fission fungus be- 

 longing to the group of butyric acid bacteria, and bearing the 

 name of Clostridium Pasteurianum. This occurs in the form of 

 rods, 1.2 jt* broad and about 5 //. long, each producing an endospore, 

 the cells thereby swelling up to the clostridium form, and storing 

 up in their interior (though not at both poles) substances that 



