THEORY OF FERMENTATION. 
H i 
M. Pasteur obtained these corpuscules, or germs, by washing ripe fruit—(grapes he first 
used)—with pure distilled water. The water was rendered slightly turbid by the presence of an 
infinite variety of minute particles ; many of them were shapeless atoms of dust, scales of epidermis, 
or spicules of crystalline matter, but many others appeared to be organized corpuscules resembling 
the spores of funguses. These organized corpuscules differed considerably from each other, and 
when M. Pasteur cultivated them, with all due care in saccharine fluids, he found them to swell and 
germinate at different times and in different ways. In an hour, and often in less time, he observed 
a copious formation of new cells, whilst small bubbles of Carbonic Acid gas were given off, 
shewing that the formation of Alcohol had already began. They were thus proved to be true yeast 
plants, or Saccharomyces. M. Pasteur traced the growth of several species of yeast plants under the 
microscope, all differing in their size of cells, shape and mode of budding, and general growth. The 
most common of these plants, to whose growth in the natural saccharine juices of fruits the formation 
of Alcohol is chiefly due, he described minutely in 1862, in the Bulletin de la SociSte Chimique , p. 67. 
These observations were fully confirmed by Dr. Rees, a German Physician and Naturalist, in 1870, 
and he first attached to them the following specific names :— 
Saccharomyces apiculatus , which is the first of them to grow, and the most minute in size : 
Saccharomyces Pastorianus , which is by far the most active and abundant, and which Dr. 
Rees named after M. Pasteur: 
And Saccharomyces ellipsoideus , which is the slowest in growth, but most persistent, and 
which is the ordinary ferment of wine. 
M. Pasteur describes minutely, from his observations, the life history of these Saccharomyces , 
their several modes of rapid development and reproduction, together with the chemical changes they 
effect by the decomposition of Glucose, such as the production of Alcohol, Glycerine, &c. These 
plants frequently take different forms, according to the varying circumstances under which they 
grow : for example, one form of Saccharomyces Pastorianus is so small that it was thought to be a 
different ferment, and was called by Dr. Rees, Saccharomyces exiguus; whilst another form was 
named by M. de Bary Dematium pullulans . 
Certain it is, that the mode of life of these plants is essentially different from that of all 
other living organisms, and the resulting chemical action is equally exceptional. Most organised 
beings live and grow by absorbing oxygen from the air and setting free carbonic acid : so do the 
Saccharomyces in the first stage of their existence ; but the air of the fluid in which they live is 
quickly exhausted, and when this happens, they obtain the oxygen essential to their growth from the 
glucose ; and in decomposing the glucose they set free more oxygen than they require ; and this, 
uniting with the hydrogen and carbon present, forms the various products of the fermentation they 
occasion. 
There are numerous other microscopic funguses, whose minute germs are always present in the 
air, ready to take their life growth in the decomposition of saccharine fluids; such as various species 
from the families Mucedines , Mucorina , Torulce , &c. These fermentations, commonly called “ after 
fermentations,” M. Pasteur calls “ diseased,” because their propagation and development is always 
attended with the loss of the Sugar or Alcohol, and with the production of some unpalatable result. 
The Cider or Perry may thus become acid, viscous (ropy), or be altogether spoilt, according as the 
germs of the several funguses which produce these results have been able to develop themselves 
within it. 
