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missed their calling; they are doing damage to us instead of
following that beneficent work for which micro-organisms
seem to have been designed. Possibly if it were not for the
pathologic forms men and animals would multiply excess-
ively upon the earth and become too crowded ; possibly they
are not such an unmixed evil after all, and yet w^e can only
regard them as an evil.
Poisons Formed by Micro=organisms.
I can only introduce the next subject and let you think
of it in the meantime—the poisons formed by micro-organ-
isms. These poisons are the waste products of which we
have spoken, and in order that you may start with a clearer
conception of how it is that some micro-organisms form
poisons and some micro-organisms grow and do not form
poisons, we may refer to the higher plants again.
You have been engaged in the study of materia medica
and in this study you have the alkaloids as prominent items.
These alkaloids are the poisonous products of the higher
plants. But poisonous material is not formed by all the
higher plants. Many of these plants are good food for men
and animals. But certain of the higher plants form the most
virulent poisons that we know in medicine. Take Strychnia,
Nux Vomica, Morphia, Curarin and various others, and we
have poisons that kill quickly, and it does not require great
concentration of these to make the man sick. I remember
very well when we used to go to the fields and gather lobelia
and other plants and make an infusion of them for use in
medicine. Now, micro-organisms form poisons in a similar
way. Very many of the micro-organisms do not form waste
products that are particularly poisonous, that are particu-
larly injurious. Many of the fruits that are decaying more
or less, containing millions of micro-organisms that are
working the destruction of the fruit, may be eaten without
any injury to the person ; in fact, most of them may be, as
most micro-organisms do not form poisons that are of any
consequence. But there are certain among them that do
form poisons, and the study of these poisons is yet, I may
say, in its infancy. We know only a few of them well, and
yet among these few we have found the most virulent poisons
that we know.
There are four kinds of microbic poisons. First, the
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