78 
IOWA ACADEMY OF SCIENCES. 
powder, but it would not overcome the force with which 
the atoms of hydrogen, oxygen and carbon are held to- 
gether. No hydrogen or oxygen gas would arise from such 
a stroke simply because the force existing between the 
atoms, known as chemical force, is so much greater. 
It is by means of this, the greatest known physical force, 
that the little plants make themselves felt. These silent 
forces are the great forces of the world. Noise is usually 
the evidence of weakness. Could we but get a rational 
view of the objects of the microscopical order of magnitude 
we would indeed see a battle royal in the building up and 
tearing down of tissues. The sharp contest for holding 
strategic and vital points, the surprising enfilading move- 
ments, and the great evolutions of unnumbered millions 
make a spectacle more wonderful that the taking of Port 
Arthur, the battle of Sedan or that of Grettysburg. 
Two hundred years ago it was a common belief that 
certain diseases should be allowed to take their course 
because it was interfering with the work of Providence to 
endeavor to prevent them. Smallpox was as universal 
then as measles and mumps are now. It was expected 
that everybody would have the smallpox, and if he survived 
it was evidence that his time to die had not come. There 
was a time when the average mind reasoned as follows; 
“Whatever is universal is right. Certain diseases are 
universal, therefore, it is right that they should be.” 
This is not the philosophy of the twentieth century. 
While the cure of disease has its origin in the remotest 
antiquity, the prevention of disease is a modern idea. It 
is not likely that the plagues of the middle ages will ever 
sweep over our civilization. The art of prevention has too 
strong a hold on public opinion. 
Thirty years ago the source and cause of typhoid fever 
was shrouded in the deepest mystery. Today this specific 
germ is well known, its characteristics well understood. 
The rapid progress in prevention of diseases is paralleled 
with our growing knowledge of bacteria. 
