98 MICROBES, FERMENTS, AND MOULDS. 



IV. TIIE MICROBES WHICH AFFECT WINE. 



The affections to which some wines are subject 

 alter their taste and quality so as often to render 

 them unfit for use. These affections ought to be 

 recognized, so that a diseased wine may not be con- 

 founded with one which is adulterated, and it is by 

 means of the microscope that we are enabled to 

 recognize the nature of these changes. Chaptal for- 

 merly ascribed them to the presence of an excess of 

 ferment, since he was unable to discover any other 

 cause. We now know from Pasteur's valuable re- 

 searches, published in his book, Etudes sur Ics vins, 

 that they are all due to the. presence of microbes 

 peculiar to each disease. 



" The source of the diseases which affect wine," 

 Pasteur writes, " consists in the presence of parasitic 

 microscopic plants, which are found in wine under 

 conditions favourable to its development, and which 

 change its nature either by the withdrawal of what 

 they take for their own nutriment, or still more by 

 the formation of fresh products which are due to the 

 multiplication of these parasites in the wine." These 

 diseases are known under the names of acescence, 

 pousse, graisse, amertume, etc. We shall review them 

 in succession. 



Mouldy or Flowered Wine. These are wines on the 

 surface of which white pellicles are formed (jieurs de 

 viri), which consist of Mycoderma vini (Figs 43 53). 



