NITROGEN FIXATION 235 



nitrogen, since it at first makes use of the traces of combined nitrogen, 

 occurring as impurities in the nutritive solution, and afterwards assimilates 

 the nitrogen of the air. According to the same authority, there are certain 

 Cyanophyceae (Nostoc, Anabaena) which behave in a precisely similar way to 

 Azotobacter, so that BEIJERINCK has been led to establish a special physio- 

 logical class of organism, to which he applies the term ' oligonitrophilous ', 

 among which he reckons Clostridium. We must note in this relation that 

 there is one great difference between BEIJERIXCK'S and WINOGRADSKY'S 

 researches, for the latter has proved the occurrence of a nitrogenous gain by 

 quantitative chemical analyses, whilst the former omits all such proof. More 

 recently WINOGRADSKY (1902, Centrbl. Bakt. II, 9, 43) has taken the same 

 view of BEIJERINCK'S work, and BEIJERINCK himself (1902, Centrbl. Bakt. II, 

 9, 3) admits that Azotobacter does not assimilate free nitrogen. His more recent 

 statements as to the real nitrogen-combining Bacteria must therefore be received 

 with a certain amount of scepticism. [It has been shown more recently still 

 that Azotobacter does assimilate free nitrogen ; the essential difference between 

 Azotobacter and Clostridium lies in the fact that the former is aerobic (compare 

 the comprehensive exposition of the subject by KOCH, 1904). Both forms occur 

 in the sea as nitrogen combiners (KEUTNER, 1904).] 



The combination of atmospheric nitrogen has been maintained for other 

 forms, e.g. for Aspergillus and Penicillium by PURIEWITSCH (1895), and for other 

 Mould-fungi by SAIDA (1901). The increase in combined nitrogen in the^cultures 

 is, however, very minute, and we must await confirmatory experiments before we 

 can pronounce definitely on the subject. CZAPEK (1902, Beitr. z. chem. Phys. 

 u. Path. 2, 559) was unable to observe any combination of free nitrogen in 

 any of his experiments with Aspergillus. The power of combining the free 

 nitrogen of the air is even more doubtful in the case of the endosporal bacillus 

 (Bacillus ellenbachensis] than in the case of the Fungi referred to ; accurate 

 investigations have indeed shown that such a capacity does not exist. In 

 spite of this, pure cultures of this bacillus are sold under the name of ' alinite ' 

 for impoverished soils ; they are said to aid in the combination of nitrogen in 

 the soil when spread over the ground. 



If as vigorous a combining of nitrogen took place in all soils as in KUHN'S 

 experiments mentioned at the beginning of this lecture, neither alinite nor 

 any artificial manuring with nitrogen would be necessary. Experience teaches 

 us the contrary, however ; generally speaking, nitrogenous manuring is in- 

 dispensable, and the Leguminosae only form an exception, to be considered 

 afterwards. The combining of nitrogen in KUHN'S fields must have been un- 

 usually vigorous, and for this there must have been some special reason. If we 

 assume that Clostridium pasteurianum was the active micro-organism concerned, 

 the carbohydrates necessary for its support must have been present in special 

 abundance, so that we are met by a problem which has not as yet been con- 

 sidered, viz. as to how Clostridium is able generally to procure sugar in nature. 

 Two sources seem possible, one from the deciduous parts and remains of culti- 

 vated plants, the other from the lower Algae, which always occur in the soil. 

 It has been clearly established that combination of nitrogen takes place re- 

 markably well in soils which are rich in Algae, from which one may conclude 

 that the Algae and Clostridium stand in intimate relations to each other, the 

 Algae obtaining combined nitrogen from the Clostridium, the Clostridium 

 receiving soluble carbohydrates from the Algae (KossowiTSCH, 1894). 



As already remarked, the Leguminosae play a special part in agricultural 

 processes, not only because they grow in sterile sandy soils without any addition 

 of nitrogenous manure, but because they actually improve such soils and 

 make them suitable for the growth of plants which do not belong to that family. 

 These peculiarities of Leguminosae were known, in part at least, to the ancients 



