222 Dynamic Theory. 



Mycoderma Aceti and Mycoderma Vini are two more fermenting or- 

 ganisms. Their work is done on alcohol, which they reduce to acetic 

 acid and water. The first is developed on the surface of any aqueous 

 liquid containing two per cent, alcohol, a little vinegar and traces of 

 alkaline and alkaline earthy phosphates. The second appears in wine, 

 making it acid and weak. The Mycoderma Aceti, a bacterium, grows 

 over the surface of the solution forming a membrane by the interlac- 

 ing of strings of cells. The cells are from . o t o 5 oo to -^^ of a mm. in 

 diameter. They are generally united in chains, and increase by cross 

 divisions fission. (See Fig. 104, n.} 



In order that the change of alcohol of the liquid into vinegar should take place, this 

 .Mycoderma must be in contact with the air and the alcohol also. The alcohol is oxi- 

 dized through the Mycoderma; that is, I should say, the plant first, or while imprisoning 

 the alcohol in the fluid under its impervious film of cells or during that operation 

 rather takes up the alcohol into its cells, where it comes into contact with the oxy. 

 gen which the cell has absorbed from the air, and thus a new compound is formed of 

 oxgen and alcohol; viz., acetic acid. The alcohol is first dehydrogenated, losing one- 

 third of its hydrogen, when it is called Aldehyde, which then absorbs one atom of 

 oxgen, forming acetic acid. Or it may form direct by adding two atoms of oxygen and 

 losing the elements of a molecule of water. 



The use of shavings in vinegar making was once supposed to furnish 

 a catalytic medium on account of their porousness, but it was demon- 

 strated by Pasteur that the shavings were covered with thin pellicles of 

 mycoderma, to which the oxidation was due. 



The action of the Mycoderma Vini is much the same as Mycoderma 

 Aceti, but under its influence the combustion of the alcohol is complete, 

 accompanied by the production of water and carbonic acid. 



These ferments act in a manner analogous to yeast, carbon in the 

 alcohol being to them the food that the carbon of the saccharine matters 

 is to the yeast. 



Another fermenting agency is called Ammoniacal ferment. Its cells 

 are much smaller than those of beer yeast. They are spherical, without 

 internal granulations, and appear to develop by budding. Their size is 



fr m 5ooo to 10000 ^ a mm - ^ n ^ s f erment act; s upon Urea, which is the 

 chief constituent of urine and the principal vehicle for the discharge of 

 surplus nitrogen from the body. The urea is transformed into ammo- 

 nium carbonate and carbonic dioxide. 



The ferment also acts upon hippuric acid, a constituent of the urine 

 of herbivorous mammals, separating it by hydration into benzoic acid 

 and glycocol. The ferment does not previously exist in the urine, but is 

 introduced by germs from the air, or it may be artificially sown. In 

 some cases of disease it has been found in the bladder, supposed to 

 have entered by way of the urethra. In one case it was thought to have 

 been introduced by a catheter. 



Butyric ferment is said to be an animal organism or infusorium of the 

 genus Vibrio. They are little cylindrical rods rounded at the extremi- 



