years. The changes
in the methods of handling market milk have been marked. The results
of these changes in influencing the quality of milk offered to the
consumer are fully discussed.

H. L. R.

E. G. H.

CONTENTS

Structure, Growth and Distribution of Bacteria 7

Methods of Studying Bacteria 20

Contamination of Milk 28

Infection of Milk with Pathogenic Bacteria 62

Fermentations of Milk 82

Preservation of Milk 113

Bacteria and Butter Making 136

Bacteria and Cheese Making 161

Bacteria in Market Milk 189

CHAPTER I.

STRUCTURE, GROWTH AND DISTRIBUTION.

=Relation of bacteriology to dairying.= The arts which have been
developed by mankind have been the outgrowth of experience. Man
first learned by doing, _how_ to perform these various activities,
and a scientific knowledge of the underlying principles which govern
these processes was later developed.

The art of dairying has been practiced from time immemorial, but a
correct understanding of the fundamental principles on which the
practice of dairying rests is of recent origin. In working out these
principles, chemistry has been of great service, but in later years,
bacteriology has also been most successfully applied to the problems
of modern dairying. Indeed, it may be said that the science of
dairying, as related to the problems of dairy manufacture is, in
large degree, dependent upon an understanding of bacteriological
principles. It is therefore essential that the student of dairying,
even though he is concerned in large measure with the practical
aspects of the subject, should acquire as complete an understanding
of these principles as possible.

While bacteriology is concerned primarily with the activities of
those microscopic forms of plant life known as the bacteria, yet the
general principles governing the life of this particular class of
organisms are sufficiently similar to those governing the molds and
other types of microscopic life that affect milk and its products to
make it possible to include all of these types in a general
consideration of the subject.

=Nature of bacteria.