understand how these diseases are propagated, just as we understand,
now, about fermentation; and that, in this way, some of the greatest
scourges which afflict the human race may be, if not prevented, at
least largely alleviated.

This is the conclusion of the statements which I wished to put before
you. You see we have not been able to have any accessories. If you
will come in such numbers to hear a lecture of this kind, all I can say
is, that diagrams cannot be made big enough for you, and that it is not
possible to show any experiments illustrative of a lecture on such a
subject as I have to deal with. Of course my friends the chemists and
physicists are very much better off, because they can not only show you
experiments, but you can smell them and hear them! But in my case such
aids are not attainable, and therefore I have taken a simple subject and
have dealt with it in such a way that I hope you all understand it, at
least so far as I have been able to put it before you in words; and
having once apprehended such of the ideas and simple facts of the case
as it was possible to put before you, you can see for yourselves the
great and wonderful issues of such an apparently homely subject.