ACID FERMENTATIONS. 355 



already in the present volume (pp. 73, 74). The Aspergillcicece 

 recognised as producers of free acids include primarily Asp. niger, 

 Penicillium luteum, and two species of Citromyces, the first of these 

 furnishing oxalic acid and the last three citric acid. 



Decided oxalic-acid fermentation has, so far, been observed 

 solely in the case of Aspergillus niger, merely indications being 

 found with Asp. ylaucus, Penicillmni ylaucum, and also with 

 certain non-Aspergillacece (Botrytis cinerea, Sclerotinia sclerotiorum, 

 and Rkizopus nigricans), the slight traces of an excess of free acid 

 being only prevented from further decomposition by immediate 

 neutralisation. In other groups of the vegetable kingdom, how- 

 ever, free oxalic acid is formed during metabolism, and this acid 

 may remain free (Rheum and also Oxalis species), though it is 

 usually thrown down at once by the calcium carbonate supplied 

 by the soil- water (Cacti, the buds and bark of various shrubs, 

 algae). The application of the term " fermentation " to the 

 process in the case of fungi does not affect its similarity of 

 character in all these cases, though, of course, it must not be 

 classed indiscriminately with the formation of oxalates. 



The mere occurrence of calcium oxalate crystals in fungi has 

 long been known, and frequently observed in cultures of Asp. 

 niger, this being also reported by SCHROTER (II.). Their origin 

 in gelatin cultures of Penicillium glaucum was mentioned by 

 A. HANSEN (I.) in 1889, and in sclerotia of the same fungus by 

 Brefeld in 1874. A. DE BARY (II.) referred to the formation of 

 soluble oxalates by Sclerotinia sclerotiorurti ; and DUCLAUX (XXII.), 

 in 1889 mentioned casually (and without any experimental proof) 

 the formation of oxalic acid or oxalates in cultures of Asp. niger 

 on different substrata. ZOPF (XIV.) in 1889 found oxalate 

 crystals in cultures of a species of yeast, and also in cultures of 

 various acetic bacteria in peptonised sugar solutions with added 

 gelatin ; and thoroughgoing observations on this point were 

 published by BANNING (I.). The proof that oxalic acid in the free 

 state is produced by fungi, especially Asp. niger, solely in presence 

 of carbohydrates or chemically allied substances, was afforded by 

 WEIIMER (V.) in 1892 ; and at the same time an attempt was 

 made to bring the previously known facts to a focus and refute 

 the budding hypotheses on the relation between the occurrence 

 of oxalic acid and the formation of protein. These dis- 

 coveries led to a series of definite determinations on the oxalic 

 fermenta tion of this fungus, the result being to rank the 

 process with other fermentations. According to WEIIMER 

 (XXVI., XXVI.a, and V.) the process goes on in the following 

 manner : 



As soon as the vegetation has developed from the sown spores, 

 the nutrient solution of the pure culture of Aspergillus at room 

 temperature begins to turn red Congo paper blue, and to liberate 

 gas in presence of calcium carbonate both certain reactions for 



