906 The American Naturalist. [November, 
from it. It is, then, to bacteria that the farmer owes his 
new process of obtaining food through a silo. 
I will pass now to the consideration of the second topic, and 
that is, the relation of bacteria to dairy matters. I have 
already once or twice before in your meetings brought up this 
question of the relation of bacteria to the dairy. At the meet- 
ing a year ago some of you may remember that we consid- 
ered the subject of the fermentations of milk, when we saw 
that all of these fermentations, most of which are very unde- 
sirable, are connected with the growth of micro-organisms. 
Now, so far as milk is concerned, bacteria are pretty much 
of a nuisance. The milkman does not want them; they pro- 
duce the souring of his milk; they make his milk bitter or 
slimy ; sometimes they make it blue, and they produce all 
sorts of abnormal fermentations which a milkman does not 
want. But I am not to consider that side of the question this 
morning, and I will pass the subject of milk and turn for a 
moment to a consideration of the relation of bacteria to but- 
ter-making and cheese-making. 
Every butter-maker is acquainted with the fact that in the 
normal process of making butter the cream is collected from 
the milk and then is allowed to ripen. It is put in some sort of 
vessels and allowed to stand in a warm place for a day or so, 
and during that time immense changes are taking place in it. 
At the end of the time the cream has become slightly soured, 
it has acquired a rather peculiar, pleasant, indescribable odor, 
and it has reached the proper condition for churning. During 
that time our microscope tells us that bacteria have been mul- 
tiplying with absolutely inconceivable rapidity. They multi- 
ply so that they increase during a day perhaps five to six 
thousand-fold. Each bacterium with which you start when 
you begin to ripen your cream produces at least six thousand 
by the end of twenty-four hours, and usually they will pro- 
duce a much larger number than that. So that bacteria are 
growing in this ripening cream with absolutely incredible 
rapidity. Now you butter-makers know that you gain some 
advantage from ripening the cream, or at least you think you 
do. You think your butter churns a little easier and that you 
