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rather you would go out from us knowing well the general
principles of bacteriology than to know many species prac-
tically and yet not understand well the principles of this sub-
ject.
The chemical processes of plants are very important to us.
I hardly know how to convey to you an appreciation of the
chemical processes of life—of the vastness of this work of
life in Nature. Think of the changes of the seasons in this
latitude. Just now the whole landscape is becoming brown
and gray ; the green coloring is passing away. When the
spring-time comes all will be changed again ; the grass will
spring up ; the trees will put out their leaves ; the flowers
will bloom ; the fields of grain will grow and ripen and will
become ready for the harvest. Think of the billions of tons
of matter that is chemically changed in these life processes.
This is an exhibition of life as a force in Nature ; life acting
as a force, taking up the elements of earth, air and water,
changing them chemically and weaving them into new chem-

ical combinations,J|^uch vastness of amount as to change the
whole face of Nanire, and-in the physical sense, building up
new physical forms, as weli^s building up new molecular
forms in the chemical sense. It is in these chemical changes
that we must study the life processes if we would understand
bacteriology.
The physiology of plant life is much the same in all its
forms. There are minor differences, of course, but the
physiology of plant life and that of animal life is much the
same in its general principles ; there are special modifica-
tions, special dififerences, but the same general principles
apply. Now, finS.lly, it will be to these processes, these chem-
ical changes, that we will most strongly draw your attention.
It is the function of the higher plants to build ; they build
great structures, the trees, the forests are reared. They give
of¥ but little in waste products, comparatively ; they build
these into the bark and into certain parts of the wood and
the leaves, and in a sense they remain with them stored up as
formed material, and they build these great structures that
seem to be enduring, and yet pass away. How do they pass
away? When the life has passed these chemical processes
are finished ; when the life goes out from the man the
physiological processes, the chemical processes that are tak-

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