ASPERGILLUS NIGER GROUP 237 



in and upon the greatest variety of substrata, including grains, forage 

 products, spoiled fruits and vegetables, exposed cotton textiles and fabrics, 

 leather, dairy products and other protein-rich substrata, and decaying 

 vegetation in the field. They are abundant in all soils examined; and from 

 studies which have been made by the authors and other investigators, it 

 would appear that they are particularly abundant in soils from tropical and 

 sub-tropical areas. 



With the possible exception of the A. flavus-oryzae group, which is of 

 great economic importance in the Orient, the black aspergilli are un- 

 doubtedly more widely used in industry than any other group of molds. 

 Since the present volume is primarily a manual designed to assist the 

 worker in the study, diagnosis, and maintenance of the aspergilli that come 

 into his hands, no attempt will be made to discuss the various fermentations 

 and other biochemical activities of the black aspergilli. However, these 

 fermentations are of great importance and will be briefly noted. For the 

 reader who is interested in these fermentations, or perchance, is actually 

 conducting them, a fairly complete list of references is presented for each 

 in the "Topical Bibliography" (Chapter XXII). In each case it has been 

 our aim to present sufficient references to provide the reader with a reason- 

 ably comprehensive guide to the literature of the field. 



Gallic Acid: Raulin and his coworkers in Paris during the early 1860's 

 identified the organism active in the production of gallic acid by the fermenta- 

 tion of gallnuts and other tannin-bearing substances. The species was 

 first discussed as Ascophora nigrans. Van Tieghem in 1867, named and 

 described the organism correctly as A. niger. Recurrent investigations 

 have been conducted on this fermentation from that period to the present 

 time (see Topical Bibliography, p. 294). 



Citric Acid: In 1917 Currie published his fundamental studies on the 

 formation of citric acid by strains of A. niger and thereby established the 

 basis for one of the most important of all industrial mold fermentations. 

 Subsequent to this, investigators in the United States and abroad have 

 made many additional and important contributions. While no attempt 

 will be made to cite all of these, the works of Bernhauer, Wehmer, Doelger 

 and Prescott, and the U. S. Department of Agriculture group, including 

 Wells, May, Moyer, Herrick, and Ward, are considered to be outstanding. 

 A selected list of references to the citric acid fermentation is presented 

 on pages 290-293. 



Fumaric Acid: Certain strains of the A. niger group produce appreciable 

 amounts of fumaric acid, and it was to one of these forms that Wehmer in 

 1918 applied the n&me A. fumaricus. At the present time, however, fumaric 

 acid is produced in industry by fermentation with species of Rhizopus 

 rather than strains of the black aspergilli (see p. 293). 



