618 VITAL ACTIONS OF THE LOWER FUNGI. 



is absent there is a plentiful formation of marsh gas in 

 marshes. This decomposition of vegetable substances, poor 

 in nitrogen, is specially designated by the term mouldiness 

 (Vermoderung) ; but the chemical meaning of this term is not 

 yet quite clear. The term decay ( Venvesung) is also at present 

 employed for several different processes ; thus Nageli uses it 

 for the destruction of organic substances by mould fungi. 

 In this, however, we have no really marked fermentative 

 action, but only a gradual consumption of the nutrient 

 materials, and hence it is better to restrict the term to putre- 

 faction in the presence of oxygen in which when the con- 

 centration and reaction of the medium are favourable the 

 mould fungi naturally help in the complete decomposition 

 of the material. Under special circumstances where suitable 

 bacteria, or a fermentescible material, or other conditions 

 for the fermentative processes are absent, the consumption of 

 the organic substances by mould, yeast, and fission fungi 

 plays the chief part ; the destruction must then, however, go 

 on correspondingly slowly, and furnish the ordinary products 

 of tissue change of the lower fungi. It would be incorrect 

 to reckon such a process among the processes of fermentation 

 or putrefaction. 



(e). Acetic Fermentation. 



Acetic By acetic fermentation we mean the process by which 



fermentation, gethylic alcohol is converted into acetic acid, and which 

 is expressed by the formula, CH 3 , CH 2 , OH (asthylic 



Material and alcohol) +0 2 = CH 3 COOH (acetic acid)+ H 2 0. Ac- 

 cording to Nageli methylic alcohol is oxidised to formic 

 acid in a similar manner. The oxygen is taken up to 

 a very much less degree when alcohol is exposed to 

 the air, and spread out over a large surface on filtered 

 paper, wood shavings, &c. ; it occurs to a greater extent 

 when spongy platinum, charcoal, and similar porous 



Fermentative bodies aid the conveyance of the oxygen. It is par- 

 ticularly energetic, however, when the development 

 of a definite fungus occurs in the alcoholic material, 

 especially when it is spread over a large surface. As to 

 the morphological characters of this fungus see p. 

 389. Along with it there are usually found other 

 fungi ; saccharomyces mycoderma often develops at the 

 commencement in greatest numbers, so that this fungus 



