tects the strange murmurs of
respiration, the fainter, more unnatural pulsations of life, and the
obscurer workings of disease; with the _spirometer_ we determine the
breathing capacity of the lungs, and thus ascertain the extent of the
inroads made by disease; the _dynamometer_ records the lifting ability
of the patient; the _thermometer_ indicates the morbid variation in the
bodily temperature; various instruments inform us of the structural
changes causing alterations in the specific gravity of fluids, _e.g_.,
the _urinometer_ indicates those occurring in the urine; and thus, as
the facilities for correct diagnosis increase, the art of distinguishing
and classifying diseases becomes more perfect, and their treatment more
certain. While physiology treats of all the natural functions, pathology
treats of lesions and altered conditions.

[Illustration: Fig. 146.
Dr. Brown's Spirometer.]

By the term _symptoms_ we mean the evidence of some morbid effect or
change occurring in the human body, and it requires close observation
and well-instructed experience to convert these symptoms into diagnostic
signs. Suppose "Old Probabilities" (as we commonly designate the
invaluable Signal Department) hangs out his warning tokens all along our
lake borders and ocean coasts; our sailors behold the fluttering symbols
indicating an approaching storm, but if no one understood their meaning,
a fearful disaster might follow. But if these signals are understood, a
safe harbor is sought and the mariner is protected. So disease may hang
out all her signals of distress, in order that they may be seen, but
unless correctly interpreted, and a remedial harbor is sought, these
symptoms are of little practical value.

Undoubtedly the reason why so many symptom-doctors blunder is because
they prescribe according to the apparent symptoms, without any real
reference to the nature of the affection. They fail to discover how far
a symptom points out the seat, and also the progress of a disease. They
do not distinguish the relative importance of the different symptoms.
The practical purpose of all science is to skillfully apply knowledge to
salutary and profitable uses. The patient himself may carefully note the
indications, but it is only the expert physician who can tell the import
of each symptom.

_Symptoms_ are within every one's observation, but only the physician
knows the nature and value of _signs_. We have read an anecdote of
Galen, who w