512 THE ASPERGILLI 



yellow, and green mold on fodder and forage subjected to dampness even from moist 

 or humid air, upon hay and grain which is only slightly above the critical water 

 content, as yellow mold upon jams, jellies, and preserves, upon masses of soft maple 

 sugar as distributed in lines of trade, upon salt fish, and on cured meats, as green 

 mold on leather; in wetter substrata, members of this group, although commonly 

 present, are overgrown by other and more rapidly growing forms. Certain A. 

 glaucus strains are active inverters of sugar; they grow well in solutions of 50 per 

 cent of sucrose in water, some of them continue their activity in sugar solutions well 

 up toward 70 per cent, and at times their mycelium is found enmeshing the crystals 

 of stored raw sugar and causing considerable deterioration. 



As a genetic group these forms have adapted themselves to growth in highly 

 concentrated media from which few other species can extract the water necessary for 

 metabolism. Correspondingly, while able to develop in wetter situations, they are 

 usually overgrown and contribute little to the decomposition as encountered. 



The dark-brown to black Aspergilli (the aggregate species A. niger) are more 

 conspicuous, grow under a wide range of environmental conditions, and produce 

 notable changes in the substratum. Investigation of their activities goes back to Van 

 Tieghem, who studied their relation to the fermentation of tannin solutions about 

 1860-65, ^^^ even then they were used in the manufacture of gallic acid by the fermen- 

 tation of crude tannin solutions. Wehmer in 1893 investigated the production of 

 oxalic acid from sugar by these organisms. This fermentation, while entirely practi- 

 cable, cannot compete commercially with other sources of oxalic acid. Following the 

 same lines of study, Molliard, Butkewitch, and Currie investigated citric acid produc- 

 tion by A. niger. Currie and Thom went further and showed that certain races or 

 strains indistinguishable morphologically from other members of the series were spe- 

 cially active in producing oxalic acid and others more active in producing citric acid. 

 Thus the way was opened for Currie's successful development of the production of 

 citric acid upon a commercial scale with granulated sugar as its raw material. Citric 

 acid from this source is now a large percentage of the total supply reaching the market. 

 Other by-products of Aspergillus fermentations are being developed at the present 

 time, among them gluconic acid, which has already been experimentally produced 

 by several workers independently. 



The diastatic power of the black Aspergilli has been utilized in producing alcoholic 

 liquors, especially in Formosa. Biochemical workers testing for various enzymes find 

 these organisms with enzymes capable of attacking many forms of organic matter. 

 The enzymic picture is a recapitulation of the distribution of the species in nature. 

 An organism limited in nature to a particular substratum or very special conditions 

 shows a limited production of enzymes, whereas a species which grows upon many 

 substrata must be capable of utilizing the wider range of products available in this 

 varied group of substrata. 



The members of the A. niger series are well adapted for factory exploitation. 

 Their morphological characters and reactions are conspicuous. They grow readily 

 under a wide range of conditions and so vigorously as to swamp minor contaminations. 

 Although their range of biochemical activity is wide, methods of controlling that ac- 



