902 The American Naturalist. [November, 
ria. The result was that after a few years a great deal of 
information had accumulated, showing that bacteria caused 
diseases. The so-called “ epidemics” are usually the result of 
bacteria, and with minds intent upon this side of the ques- 
tion scientists did not pay much attention to the good that 
bacteria might do in the world. It was more interesting to 
study disease. People are very much interested when you 
begin to tell them why it is that they have small-pox, why it 
is that they have yellow fever; the other side of the matter, 
however, is not so interesting. 
But the fact is that the bacteria story has only been half 
told, and thus far it is the smaller half that has been told, if 
there is such a thing as the smaller half. It is true that bac- 
teria are occasionally injurious to us, but itis equally true that 
they are of direct benefit to us. Hitherto we have looked upon 
bacteria as belonging to the medical profession ; we think the 
doctors ought to know about them because they produce dis- 
ease, but ordinary people do not need to bother themselves 
with these things. ButI think before I get through with 
my talk this morning you will see that bacteria have a very 
much closer relation to you as farmers than they do to the 
doctors. It is the farmer to-day who ought to understand bac- 
teriology. It is well enough for the medical man to under- 
stand the subject also, but bacteriology has already become a 
medical subject, while the agriculturist has generally neglected 
it. 
I propose in my talk this morning to point out to you afew 
of the benefits which you as farmers derive from the agency 
of these microscopic organisms. I shall divide the subject 
into four heads. First, miscellaneous: At the very outset I am 
going to say a word or two in regard to yeasts. Now, yeasts 
are not bacteria, but they are microscopic plants closely related 
to bacteria, and their agency in nature is very similar to that 
of bacteria in some respects; so I shall say a word or two in 
regard to them. 
What is the function of yeasts? Yeasts are plants which 
have the power of growing in sugar solutions, and while grow- 
ing there they break the sugar to pieces and produce from it 
