354 CHEMICAL ACTIVITY OF ASPERGILLACE^E. 



apply the term " acid fermentation " is a rare occurrence ; and 

 up to the present this is the only family of JSamycetes in which 

 this process is carried on in the same way as by the bacteria. 

 Just as in the latter case the chief products of this fermentation 

 are acetic acid, butyric acid, and lactic acid, so with the Eumycetes 

 the products are oxalic acid and citric acid. In the case of 

 phanerogams, similar processes furnish preferably citric acid, 

 tartaric acid or malic acid. The accumulation of such acids in 

 any appreciable quantity, whether in the vacuoles of higher 

 plants or in the nutrient solution of micro-organisms, is invariably 

 a physiological peculiarity confined to certain species or families 

 (Aurantiacece, Crassulacece, Vitacece, &c.), and one that is difficult 

 to analyse closely. In the majority of cases the free organic 

 acid is merely an intermediate product, which is afterwards 

 decomposed by complete oxidation ; and the question whether 

 the formative stage has been traversed too rapidly or the decom- 

 position stage too sluggishly must remain open for the present. 

 Of course, the presence of salts of organic acids, which are 

 commonly met with, does not necessarily imply acid fermentation, 

 since the occurrence of these salts does not argue the pre- 

 existence of free acids, but is more frequently the result of the 

 availability of bases during metabolism. 



At present we are probably only on the threshold of knowledge 

 with regard to acid fermentation, and continued systematic investi- 

 gation may reveal both additional fungi and acids concerned in 

 the process. Even now a few reports still, however,; incomplete 

 are available on the point. Thus, it is known that Asp. oryzcv 

 will acidify saccharine nutrient media, though the nature of the 

 acid has not been determined. GRAF (I.) found the acidity of a 

 28-days-old culture on wort to be equivalent to 40 c.c. of deci- 

 normal baryta per 20 c.c. of culture liquid, as compared with an 

 acidity of only 2.45 c.c. in the case of " Penicittium glaucum" and 

 of 56.6 c.c. with Asp. niger, for the same volume of liquid. The 

 fact discovered by LIND (I.), ih&tAsp. niger and " Penic. glaucum " 

 will corrode thin plates of lime (see p. 61, vol. ii.), is apparently 

 as in the case of algae, rich in calcium oxalate at least partly 

 due to such acidity. 



The statement by SANGUINETTI (I.) that formic acid and acetic 

 acid are present in cultures of Asp. oryzce, lacks probability, and 

 should be confirmed by means of pure cultures ; and the same 

 applies to HEINZ'S (II.) assumption that acetic acid is produced 

 by Asp. niger. Moreover, the statement that a so-called Lacto- 

 myces fungus will ferment sugar solutions to lactic acid must be re- 

 garded as lacking both proof and probability, although the German 

 authorities granted a patent (No. 118. 063, of Feb. 26, 1901) 

 for it, especially as no thread fungi have yet been found to produce 

 that acid. This opinion is endorsed by CZAPEK (IV.). The souring 

 of culture liquids by certain Mucorinece has been dealt with 



