98 Fermentation and Kindred Phenomena. 



with the spirit. Pasteur has proved, however, that the deter- 

 mining cause of the oxidation is a definite ferment which has 

 received the name of my coder ma aceti. It consists of minute 

 rods or chains of rods, which often become felted together, 

 forming a membrane somewhat like moist paper pulp to the 

 naked eye, and this membrane is frequently found on the surface 

 of the acidifying liquor, and is called the " mother of vinegar," 

 or simply the " vinegar plant." Pasteur proved that the change 

 of spirit into vinegar is really caused by the action of this fer- 

 ment — and not by the simple action of the air — by a very 

 elegant experiment. He allowed weak spirit to trickle down 

 string (which is of course highly porous), and showed that in 

 spite of its porosity no oxidation occurred, even after a month. 

 He then steeped the cord in a liquid containing a pellicle of the 

 mycoderma, some of which adhered to it, and then as before 

 allowed the spirit to trickle down it, when it was rapidly 

 acetified. 



The manufacture of vinegar is carried out at Orleans in accord- 

 ance with Pasteur's discoveries, the ferment being sown on the 

 surface of the wine or beer. When the surface is covered with 

 the membrane, the alcohol begins to acetify. From time to 

 time fresh wine or beer is added, and when the acetification has 

 terminated the membrane is collected, washed, and employed 

 for a new operation. 



I have not sufficient time to describe all the organisms which 

 are capable of producing definite and well ascertained chemical 

 reactions, and can merely mention one or two others. The 

 ammonia ferment, which has the power of producing am- 

 monia or hartshorn from urea, a substance abundantly excreted 

 from carnivorous animals. 



The nitre ferment, present in soil which oxidises ammonia to 

 nitric acid. 



The glycerine-ethyl ferment, which converts glycerine into 

 spirit, &c. 



Organisms causing the production of colouring matters. — 

 Certain organisms belonging to the group of schizomycetes 

 have the property of producing definite colouring matters, 



