VETERINARY MATERIA MEDICA. 
39 
loss of blood. There is an alternate play of the power of absorp¬ 
tion between different parts. When intestinal absorption is active 
that of the skin diminishes. W hen the animal is fasting*, the 
inhalent vessels of the skin are active. This will point out the 
proper time to employ medicines that are designed to be absorbed 
through the medium of the skin. Thus under a severely re¬ 
stricted diet many serous effusions and chronic enlargements 
disappear. 
The structure of the different tissues—their permeability— 
their vitality—the morbid condition in which they may be, will 
powerfully influence the phenomena of absorption. It is less 
readily carried on through the skin than the mucous membranes, 
and less through them than the serous membranes. If the skin 
be deprived of the cuticle by means of blisters, many substances 
will be rapidly absorbed,—a very important consideration in cases 
of tetanus or impossibility of swallowing. Sometimes this power 
of absorption, thus increased, is followed by unpleasant effects, 
as in the production of strangury from a blister. 
The nervous system is a powerful agent in transmitting the 
influence of medicines, not as conveying*, like the arteries, the 
substance of the drugs, but propagating their influence by an 
action purely vital. All organs are not equally powerful in pro¬ 
ducing this transmission of influence. The stomach, from its 
connexion with the brain, the lungs, and the abdominal viscera, 
holds the first rank. In some cases the medicine has scarcely 
come in contact with this viscus, ere the most distant organs 
sympathize, while, perhaps, the neighbouring ones may be 
unaffected. 
This sympathetic action, however, is not so general as that 
which is to be traced to absorption ; but often these two princi¬ 
ples, so distinct in theory, succeed each other so rapidly, and 
are so intimately associated, that we know not to which the 
effect is to he principally traced. There are some substances, 
the influence of which is propagated so quickly, and in so re¬ 
markable a manner, that they seem to have a perfectly specific 
action on the nervous system. The hydrocyanic acid affords an 
. illustration of this. 
The action of medicines on the animal economy gives rise to 
a series of phenomena, which arc designated by the common 
title of effects. These differ in their nature, and intensity, and 
relations with each other; and often appear in succession, and 
therefore we speak of the primary or immediate, and the se¬ 
condary or consecutive eff ects of them. The first are the direct 
effects of the medicine on certain organs,— easily foreseen, and 
easily produced, and in health as well as in sickness:—the 
