thermometer
has occasionally given rise to needless alarm, but almost invariably it
may be interpreted with great certainty. Often it dispels unnecessary
anxiety as in a twinkling by its negative indication, and surely it is
to be credited with being distinctly diagnostic in those diseases of
which it has itself established the 'curve.'" By the thermometric
"curve" of a disease is understood the general visual impression made by
the graphic chart of a temperature record--the course of a zigzag line
connecting the points indicated by the various individual observations.

Numerous other instruments of precision are now in constant use, among
the most wonderful of which perhaps is the ophthalmoscope, whereby we
are enabled to subject the retina and the intervening media of the eye
to minute visual examination. There is not an organ of the body that is
not now interrogated daily in the way of physical diagnosis, and we even
examine separately the secretion of each of the two kidneys. In
addition, there are multitudinous specific signs of which we were not
long ago in complete ignorance. To cite only one of these, there is
Widal's agglutination test, by which the bacteriologist can usually make
a diagnosis of typhoid fever far in advance of the time at which it
could otherwise be distinguished. The use of the Roentgen rays in
diagnosis was one of the crowning achievements of the century, and now
we seem about to enter upon a course of their successful employment in
the treatment of disease--even some forms of cancer--as well as in its
detection.

Beyond the vermin that infest the skin and the hair, tapeworm, and a few
other intestinal worms, little if anything was known of morbific
parasites before the Nineteenth Century; but the labors of Van Beneden,
Kuechenmeister, Cobbold, Manson, Laveran, and others have now established
the causal relationship between great numbers of animal parasites--gross
and microscopic--and certain definite morbid states. This has led to a
great increase in our knowledge of the connection between the parasites
of the lower animals and grave disease in human beings, and on this
knowledge rest many of the precautions that we are now able to take
against the spread of such disease. From the consideration of animal
parasites as the direct causes of disease, we naturally come to the
contemplation of the subject of insects as the carriers of disease. The
later years of the century have witnessed the de