from an Agricultural and Veterinary Point of Vieu\ 57 
air. Yet the ferment-cells multiply with extraordinary rapidity, 
notwithstanding the entire absence of air or free oxygen ; while 
their activity during this period is exhibited in the enormous 
difference between their weight, when collected as yeast at the 
termination of the process, and the weight of the " must " or sugar 
which has fermented, and been transformed into alcohol, car- 
bonic acid, and some other products. It has been computed 
that a pound of the ferment will cause the transformation of one 
hundred and fifty pounds of sugar into alcohol. 
Fig. 3. — Torula or Saccharomyces (Yeast Fungus). 
@ 
In the lower part of ihe figure an ascosporc and four isolated spores (after Eees) are shown. 
Magnifying power about 700. 
In shallow vessels, Pasteur found that the ferment was even 
more active than in deep vats, though exposed to the air ; but 
then much less sugar was decomposed — not more than five or 
six pounds. It was thus demonstrated that the more free oxygen 
the ferment consumes, the less does it act as a ferment ; while 
the more completely its vital functions are carried on inde- 
pendently of air or free oxygen, the greater is its power of 
transforming or decomposing sugar. Life without air, and the 
process of fermentation, are correlative incidents ; though it is to 
be observed that oxygen is essential to the life and growth of 
the ferment-cell, and when not obtainable from the air, it takes 
it from the saccharine matter, which contains it ; in doing this 
it produces alcohol, which is merely sugar minus some of its 
oxygen. This ferment-cell or vibrio, and others of its kind, 
can only live and multiply without air so long as it receives a 
sufficient quantity of suitable food ; when this is consumed, it 
dies, and further transformation of the matter ceases, unless 
another kind of organism finds access. 
These investigations led Pasteur to recognise two classes of 
microscopic organisms — one which requires air or free oxygen 
