_In health_ the temperature of the body is maintained at a mean of about
98.4° F. (37° C.) by the heat-regulating mechanism. It varies from hour
to hour even in health, reaching its maximum between four and eight in
the evening, when it may rise to 99° F., and is at its lowest between
four and six in the morning, when it may be about 97° F.

The temperature is more easily disturbed in children than in adults, and
may become markedly elevated (104° or 105° F.) from comparatively slight
causes; in the aged it is less liable to change, so that a rise to 103°
or 104° F. is to be looked upon as indicating a high state of fever.

A sudden rise of temperature is usually associated with a feeling of
chilliness down the back and in the limbs, which may be so marked that
the patient shivers violently, while the skin becomes cold, pale, and
shrivelled--_cutis anserina_. This is a nervous reaction due to a want
of correspondence between the internal and the surface temperature of
the body, and is known clinically as a _rigor_. When the temperature
rises gradually the chill is usually slight and may be unobserved. Even
during the cold stage, however, the internal temperature is already
raised, and by the time the chill has passed off its maximum has been
reached.

The _pulse_ is always increased in frequency, and usually varies
directly with the height of the temperature. _Respiration_ is more
active during the progress of an inflammation; and bronchial catarrh is
common apart from any antecedent respiratory disease.

_Gastro-intestinal disturbances_ take the form of loss of appetite,
vomiting, diminished secretion of the alimentary juices, and weakening