110 NUTRITION AND METABOLISM. 



species are able to produce a little acid. The most characteristic quality 

 of molds is their great oxidizing power which enables them to use many 

 different kinds of organic substances for food. Besides this oxidizing 

 quality, they have also the power of causing acid fermentation or alco- 

 holic fermentation. The acids produced by molds are mostly di- and 

 tribasic. Besides the acetic acid, oxalic and citric acids are produced 

 by molds. Oxalic acid is formed, especially by the Aspergillacea, in 

 large quantities, if some alkali, like calcium carbonate, is present to 

 neutralize the free acid. Aspergillus niger, the typical oxalic-acid mold, 

 is supposed to oxidize dextrose according to the following equation: 



C 6 H 12 6 + 9 = 3(COOH) 2 + 3 H 2 



The yield of oxalic acid is, however, only one-half of what could be 

 expected from the above equation, because of the very pronounced 

 oxidizing qualities of this mold; it will oxidize part of the dextrose, or of 

 the acid, completely to carbon dioxide and water. If the acid is not 

 neutralized, the mold will finally oxidize all the oxalic acid to carbon 

 dioxide and water. 



Citric acid (CH 2 (COOH)COH(COOH)CH 2 COOH) is formed by 

 many molds. Some of them produce it in such quantities as to render 

 possible the manufacture of citric acid from glucose by the use of molds. 

 The process can be expressed by the following equation: 



C 6 H 12 6 + 3 0= C 6 H 8 7 + 2 H 2 



The mold uses, however, about twice as much sugar as would be 

 expected from this formula, because of its strong oxidizing power. 



This discussion involving the products of the decomposition of sugars 

 is far from complete, but aims to touch the most common fermentations. 



ALCOHOLS. Besides the carbohydrates, another group of food sub- 

 stances has to be mentioned which is closely related to the sugars, namely 

 the higher alcohols. The two main representatives are mannit (CH 2 OH.- 

 CHOH.CHOH.CHOH.CHOH.CH 2 OH) and glycerin (CH 2 OH.CHOH.- 

 CH 2 OH). Mannit differs from the simplest sugars only by having two 

 additional hydrogen atoms which indicates that the aldehyde or ketone 

 group of the sugar is changed into an alcohol group in the mannit. The 

 products of mannit fermentation are very similar to those of sugar fer- 

 mentations. Different organisms give different products among which 

 alcohol and acetic acid prevail. The Strept. pneumonia decomposes it 

 in the following way: 



