vin BACTERIA AS FERMENTS 91 



tartrate instead of decomposing proteid. It has also been 

 shown that some Bacteria can go further and make use of 

 nitrates as a source of nitrogen, and of a carbonate or even 

 of carbon dioxide as a source of carbon : in other words, 

 they are able to live upon purely inorganic matter in spite 

 of the fact that they contain no chlorophyll. Some species 

 may even multiply to a considerable extent in distilled water. 



But pari passu with their ordinary nutritive processes, 

 many Bacteria exert an action on the fluids on which 

 they live comparable to that exerted on a saccharine 

 solution by the yeast-plant. Such microbes are, in fact, 

 organized ferments. 



Every one is familiar with the turning sour of milk. This 

 change is due to the conversion of the milk-sugar into 

 lactic acid. 



C 6 H 12 6 = 2(C 8 H 6 8 ), 

 Sugar. Lactic Acid. 



The transformation is brought about by the agency of 

 Bacterium lactis, a microbe closely resembling B. termo. 



Beer and wine are two other fluids which frequently turn 

 sour, there being in this case a conversion of alcohol into 

 acetic acid, represented by the equation 



C 2 H 6 O + O 2 = H 2 O + C 2 H 4 O 2 , 



Alcohol. Oxygen. Water. Acetic Acid. 



The ferment in this instance is Bacterium aceti, often 

 called My coder ma aceti, or the " vinegar plant." It will 

 be noticed that fti this case oxygen enters into the reaction : 

 it is a case of fermentation by oxidation. 



Putrefaction itself is another instance 01 fermentation 

 induced by a microbe. Bacterium termo the putrefactive 

 ferment causes the decomposition of proteids into simpler 

 compounds, amongst which are such gases as ammonia 



