the way of the health-officer when he endeavors to
attack and break up an epidemic of measles, whooping-cough, or
chicken-pox.

It cannot be too strongly emphasized that, mild and in their immediate
results trifling, as most of these "little diseases" are, they are
genuine members of that class of pathologic poison-snakes, the
germ-infections; that when they bite, they bite to kill; that two to
five times in every hundred they do kill; that, like all other
infections, they are capable of inflicting serious and permanent damage
upon the great vital organs, the heart, the kidneys, the liver, and the
brain; and that they are the very jackals of diseases, tracing down and
pointing out the prey to the lions that work in partnership with them.
With whatever we may treat measles and whooping-cough, _never_ treat
them with contempt!

The next conception of the "whyness" of children's diseases was that as
one star differs from another in glory, so does one germ differ from
another in virulence; that the germs of these particular diseases just
happened to be from the beginning unusually mild and at the same time
highly contagious, so that they remained permanently scattered about
throughout the community, and attacked each successive brood of newborn
children as quickly as they could conveniently get at them. Being so
mild and so comparatively seldom fatal, little or no alarm was excited
by them and few efforts made to check their spread, so that they
continued to flourish, generation after generation. Upon this theory the
germs of measles, chicken-pox, whooping-cough, mumps, would be in
something like the same class as the numerous species of bacteria and
other germs that normally inhabit the human mouth, stomach, and
intestines; for the most part, comparatively harmless parasites, or what
are technically now known as "_symbiotes_" (from two Greek words,
_bios_, "life," and _syn_, "with"), a sort of little partners or
non-paying boarders, for the most part harmless, but occasionally
capable of making trouble. There are scores of species of such germs in
our food-canals, some of which may be even slightly helpful in the
process of digestion. Only a very small per cent of the bacilli of any
sort in the world are harmful; the vast majority are exceedingly
helpful.

There is evidently some truth in this view of children's diseases,
especially so far as the reason for their steady persistence and
undiminished spread is concerned