CLOSTRIDIUM PASTEURIANUM 271 



by the Clostridium. Winogradsky observed two species of such assistant 

 organisms, detailed mention of which can, however, be omitted, it being sufficient 

 for our purpose to have referred to this new case of symbiosis. 



Whether the just-named faculty of fixing nitrogen is also possessed by the 

 organisms akin to Clostridium Pasteurianum, e.g. Prazmowski's Clostridium 

 butyricum, still remains undermined. WIXOGRADSKY (III.) examined fifteen 

 species of soil bacteria in this connection, with only negative results. In the 

 higher fungi K. PURIEWITSCH (I.), in an improved continuation of Berthelot's 

 researches, showed that both Aspergillus niger and Penicillium glaucum fix free 

 nitrogen. Their potency is, however, but slight, and is not to be compared 

 with that of Clostridium Pasteurianum, since it is not manifested in media 

 devoid of nitrogen. According to H. JUMELLE (I.), Spirillum luteum, also, is 

 capable of thriving in media free from nitrogen. 



The proof of the fact that the fixation of free nitrogen occurs in the soil 

 affords a new possible explanation of the activity of the nodule bacteria of the 

 Leguminoscf, viz., that the actual absorption of the free nitrogen goes on outside 

 these root formations ; substances unassimilable by higher plants being formed, 

 and then converted into an assimilable form by the nodule bacteria. This 

 provisional interpretation, which will not encroach on future research, is not 

 without its analogies; one need only recall the Mycorhiza, discovered by Frank 

 on the rootlets of the majority of forest trees (Cupuliferce, Conifarcp), heaths 

 (A'/v'cYtcer*), &c., and in regard to which the most important discoveries made up 

 to the year 1888 will be found briefly reviewed in a treatise by F. BEXECKE (II.). 



The great importance to General Physiology of the researches reported 

 above will be readily appreciated, since they have brought to our knowledge 

 organisms which dispense with combined nitrogen as a food-stuff, and are 

 consequently of the greatest importance in the economy of Nature, by revealing 

 the means for maintaining the circulation of nitrogen. Large quantities of 

 this element are daily liberated by the activity of both de-nitrifying and nitrifying 

 bacteria, and restored to the atmosphere, the result being that the stock of 

 nitrogenous compounds, so essential to the nutrition of all other plants and all 

 animals, becomes reduced. To compensate and reverse this loss is the task of 

 the nitrogen-fixing fungi, which, for this reason, must be regarded as the 

 benefactors and foster-mothers of all other living creatures. 



