Men yet live who can remember when all of our knowledge of disease was
acquired by the unaided use of the eye, the ear, and the touch. The
physician felt the pulse, and judged of fever by the sense of warmth. He
looked at the skin and tongue and the secretions, and formed
conclusions, more or less just in proportion to the educated acuteness
of his senses and the use he made of these accumulations of experience.
The shrewdness of the judgments thus formed shows us, to our wonder, how
sharply he must have trained his senses, and has led some to suspect
that our easier and more exact methods and means may have led us to
bestow less care in observation than did these less aided and less
fortunate students. The conclusion is, I am sure, erroneous, and I am
confident that the more refined the means the more do they train us to
exactness in all directions, so that even what we now do with the eye,
ear, or hand alone is better and more carefully done than when the
senses had none of the training due to the use of instruments of
precision. I may add that the results of their employment have also made
it easy in many cases to dispense with them, and to interpret readily
what has been won by the unassisted sense.

The history of precision in medicine is worth the telling, if only to
teach the lay reader something of that vast struggle to know the truths
of disease, which is little understood beyond the ranks of the most
scholarly of my profession. The first step was due to Galileo. In 1585
he used his pendulum to record the pulse, in a fashion at which we smile
to-day, and yet what he tried to do was the birth of precision in
medicine. Keeping a finger on the pulse, he set a pendulum in motion. If
it went faster than the pulse, he put the weight a little lower, or as I
may state it to make it clearer, he lengthened the pendulum. At last
when it moved so as to beat equal time with the pulse, he measured the