Reprinted February, 1920


PRINTED IN AMERICA




PREFACE


The struggle of man against his unseen and silent enemies, the lower or
bacterial forms of life, once one becomes alive to it, has an
irresistible fascination. More dramatic than any novel, more sombre and
terrifying than a battle fought in the dark, would be the intimate
picture of the battle of our bodies against the hosts of disease. If we
could see with the eye of the microscope and feel and hear with the
delicacy of chemical and physical interactions between atoms, the heat
and intensity and the savage relentlessness of that battle would blot
out all perception of anything but itself. Just as there are sounds we
cannot hear, and light we cannot see, so there is a world of small
things, living in us and around us, which sways our destiny and carries
astray the best laid schemes of our wills and personalities. The gradual
development of an awareness, a realization of the power of this world of
minute things, has been the index of progress in the bodily well-being
of the human race through the centuries marking the rebirth of medicine
after the sleep of the Dark Ages.

In these days of sanitary measures and successful public health
activity, it is becoming more and more difficult for us to realize the