Page 21 - My FlipBook

DEFINITION OF SUBJECTS. 19
rapid effect than when administered by the mouth internally.
Internally, by the mouth ; by inhalation ; by the rectum^ when it is
inadvisible to administer them by the mouth.
The changes which medicines undergo when taken into the
system depend upon the condition of the system, the temperature
of the body, the food and drink, and the tendency of medicines
to combine with other substances and form different compounds.
The rapidity with which medicines enter the circulating fluid is
governeJ by their composition. The crystalloid substances pass
into the blood very readily, while colloid substances enter slowly,
or not at all. Arsenious acid is an example of the crystalloid.
Corrosive poisons not only destroy life, but also the parts with
which they come in contact, while other poisons destroy life
alone. The blood conveys medicines to different parts of the
body, and during such a passage they change the character and
composition of the blood ; and are eliminated from the system
bv the excretory organs, such as the lungs, kidneys, skin, urinary
and salivary organs. The form in which medicines are adminis-
tered and applied, also modify their effects.
The action of drugs is also modified by pharmaceutical combi-
nation, as the joint effect of two medicines is different from that
one of them may cause, for opium given with mercury will pre-
vent the purgative action of the mercury. The action of medi-
cines may be direct so as to produce local effects ; or it may be
general or indirect when the entire body, or remote organs are
affected. A large number of medicines operate physically on the
bodv and affect remote parts through the agency of the nervous
svstem ; among such are electricity, cold, heat, mechanical irri-
tants, etc., which affect remote parts by the influence of the
cerebro-spinal and ganglionic systems. The afferent or sensory
nerves convey impressions to the nerve-centre, and the efferent
or motor nerves transmit impressions from the centre to muscles,
vessels, glands, etc., and the effects of medicines are transmitted
to the brain, producing an excitement of a nerve-centre and a
reflex action is carried along the efferent nerves, producing cer-
tain symptoms. The effects of medicines are modified by the
age of the patient, as young children require small doses as a