eriology. This was the now
world-famous discovery by Robert Koch that consumption and other forms
of tuberculosis were due to the attack of a definite bacillus. No
tubercle bacillus--no consumption.

At first sight this discovery appeared to be anything but encouraging.
In fact, it seemed to make the situation and the outlook even more
hopeless. And when within a few years it was further demonstrated in
rapid succession that most of the diseases of the spine in children, of
the group of symptoms associated with enlarged glands or kernels in the
neck and known as "scrofula" or struma, most cases of hip-joint disease,
of white swelling of the knee, a large percentage of chronic ulcerations
of the skin known as _lupus_, a common form of fatal bowel disease in
children, and many instances of peritonitis in adults, together with
fully half of the fatal cases of convulsions in children, were due to
the activity of this same ubiquitous bacillus, it looked as if the enemy
were hopelessly entrenched against attack. And when it was further found
that a similar bacillus was almost as common a cause of death and
disease in cattle, particularly dairy cattle, and another in domestic
fowls, it looked as if the heavens above and the earth beneath were so
thickly strewn and so hopelessly infested with the germs that to war
against them, or hope to escape from them, was like fighting back the
Atlantic tides with a broom.

But this chill of discouragement quickly passed. Our foe had come down
out of the clouds, and was spread out in battle array before us, in
plain sight on the level earth. We were ready for the conflict, and
proposed to "fight it out on this line if it takes all summer." It was
not long before we began to see joints in the enemy's armor and
weaknesses in his positions. Then, when we lowered our field-glasses and
turned to count our forces and prepare for the defense, we discovered
with a shock of delighted relief that whole regiments of unexpected
reinforcements had come up while we were studying the enemy's position.
These new allies of ours were three of the great, silent forces of
nature, which had fallen into line on either side and behind us, without
hurry and without excitement, without even a bugle-blast to announce
their coming.

The first was the great resisting power and vigor of the human organism,
which we had gravely underestimated. The second, that power of
adaptation to new circumstances, including even