308 EFFECT OF CfHEMICAL AGENTS [Cn. XI 



nitrogen is a possible food. Is it actually made use of ? This 

 question has until recently usually been answered in the nega- 

 tive, and this conclusion was the more readily accepted since 

 nitrogen is a notoriously inert gas. 



Another view, however, has within recent years come to 

 obtain. It developed in this wise. It had long been known 

 that land which has lain fallow or on which clover or other 

 leguminous crops have been reared is in a way strengthened as 

 if fertilized, and it was also known that this strengthening is 

 due to the fact that the soil acquires nitrogen from the air 

 and " fixes " it in the form of nitrates. While the studies of 

 PASTEUR on fermentation, since 1862, had paved the way for 

 the interpretation of the process, the fact that it is due to organ- 

 isms was first proved by SCHLOSING and MLTNTZ ('77, '79). 

 This proof they made by chloroforming a certain mass of nitri- 

 fying earth and finding that the nitrifying process thereupon 

 ceased. Later, they isolated a form of bacteria which had 

 the nitrifying property. Their results were quickly confirmed 

 and extended by others, notably BERTHELOT ('85, '92, etc.), in 

 a long series of investigations, so that there is now no question 

 that the nitrification of the earth is brought about by the 

 activity of bacteria, perhaps of several species. 



The results thus gained were extended to some of the higher 

 fungi by FRANK ('92, p. 596). 



Spores of Penicillium cladosporioides were sown in a nutritive solution of 

 pure grape sugar and mineral salts, completely free of nitrogen, and in the 

 presence of air which had been freed from ammonia by passing through 

 sulphuric acid. The fungi grew, but not so rapidly as those in a solution 

 containing nitrogenous compounds, and produced a mass of hyphae. These 

 hyphse, when tested, yielded ammonia. One such culture solution of 65 cc. 

 volume became filled with the fungus mass in ten months and yielded 0.0035 

 gramme of nitrogen, which must have been derived from the air. 



As similar results have been gained for other molds by 

 BERTHELOT ('93) and for Aspergillus and Penicillium glau- 

 cum by PURIEWITSCH ('95), we seem almost justified in pre- 

 dicting that the capacity for assimilating free, atmospheric 

 nitrogen will prove to be a characteristic of all fungi. 



Now if it is conceded that some organisms can make use of 

 the nitrogen of the air, it is clear that the a priori objection to 



