ention is made of some of the more important parts which
microoerganisms take in the preparation of foods.

30. Insoluble Ferments.--Insoluble ferments are minute, plant-like
bodies of definite form and structure, and can be studied only with the
microscope.[1] They are developed from spores or seeds, or from the
splitting or budding of the parent cells. Under suitable conditions they
multiply rapidly, deriving the energy for their life processes from the
chemical changes which they induce. For example, in the souring of milk
the milk sugar is changed by the lactic acid ferments into lactic acid.
In causing chemical changes, the ferment gives none of its own material
to the reacting substance. These ferment bodies undergo life processes
similar to plants of a higher order.

[Illustration: FIG. 8.--LACTIC ACID BACTERIA, MUCH
ENLARGED. (After RUSSELL.)]

All foods contain bacteria or ferments. In fact, it is impossible for a
food stored and prepared under ordinary conditions, unless it has been
specially treated, to be free from them. Some of them are useful, some
are injurious, while others are capable of producing disease. The
objectionable bacteria are usually destroyed by the joint action of
sunlight, pure air, and water.

31. Soluble Ferments.--Many plant and animal cells have the power of
secreting substances soluble in water and capable of producing
fermentation changes; to these the term "soluble ferments," or
"enzymes," is applied. These ferments have not a cell structure like
the organized ferments. When germinated seed, as malted barley, is
extracted, a soluble and highly nitrogenous substance, called the
diastase ferment, is secured that changes starch into soluble forms. The
soluble ferments induce chemical change by causing molecular disturbance
or splitting up of the organic compounds, resulting in the production of
derivative products. They take an important part in animal and plant
nutrition, as by their action insoluble compounds are brought into a
soluble condition so they can be utilized for nutritive purposes. In
many instances ferment changes are due to the joint action of soluble
and insoluble ferments. The insoluble ferment secretes an enzyme which
induces a chemical change, modified by the further action of the soluble
ferment. Many of the enzymes carry on their work at a low temperature,
as in the curing of meat and cheese in cold storage.[14]

32. General Relationship of Chemical, Physical,