in the seventeenth century.
Nevertheless, it does not seem to have become sufficiently common to be
distinctly recognized until it was named as a definite disease, and
given the title which it now bears, by the celebrated French physician,
Bretonneau, about eighty years ago. Since then it has become either more
widely recognized or steadily more prevalent, and it is the general
opinion of pathologists that the disease, up to some thirty or forty
years ago, was steadily increasing, both in frequency and in severity.

So that we have not to deal with a disease which, like the other
so-called diseases of childhood, has gradually become milder and milder
by a sort of racial vaccination, with survival of the less susceptible,
but one which is still full of virulence and of possibilities of future
danger.

Unlike the other diseases of childhood, also, one attack confers no
positive immunity for the future, although it greatly diminishes the
probabilities; and, further, while adults do not readily or frequently
catch the disease, yet when they do the results are apt to be
exceedingly serious. Indeed, we have practically come to the conclusion
that one of the main reasons why adults do not develop diphtheria so
frequently as children, is that they are not brought into such close and
intimate contact with other children, nor are they in the habit of
promptly and indiscriminately hugging and kissing every one who happens
to attract their transient affection, and they have outgrown that
cheerful spirit of comradeship which leads to the sharing of candy in
alternate sucks, and the passing on of slate-pencils, chewing-gum, and
other _objets d'art_ from hand to hand, and from mouth to mouth.
Statistics show that of nurses employed in diphtheria wards, before the
cause or the exact method of contagion was clearly understood, nearly
thirty per cent developed the disease; and even with every modern
precaution there are few diseases which doctors more frequently catch
from their patients than diphtheria. It is a significant fact that the
risk of developing diphtheria is greatest precisely at the ages when
there is not the slightest scruple about putting everything that may be
picked up into the mouth,--namely, from the second to the fifth
year,--and diminishes steadily as habits of cleanliness and caution in
this regard are developed, even though no immunity may have been gained
by a mild or slight attack of the disease. The tendency to