act. If the poison exerts a remote
influence alone, the action is quite different, little or no local effect
being produced upon the digestive organs.

To produce an effect on some part of the body distant from the channel of
entrance, a poison must have been absorbed and carried in the blood to the
central nervous system or other region involved. The poisonous effect of
any substance is modified by the quantity used; by its chemical
combinations; by the part of the animal structure with which it comes in
contact; by the physical condition of the subject; and also by the rapidity
with which the poison is excreted. As an illustration, opium may be given
with safety in much larger doses to an animal suffering from acute pain
than to one free from pain, and to an adult animal with greater safety than
to a young one. The rapidity with which the poison is absorbed, owing to
the part of the body with which it is brought in contact, is also an
important factor. So marked is this quality that some agents which have the
power of destroying life with almost absolute certainty when introduced
beneath the skin, may be taken into the stomach without causing
inconvenience, as curara, the arrow poisons, or the venomous secretion of
snakes. Other agents in chemical combination may tend to intensify, lessen,
or wholly neutralize the poisonous effect. For example, arsenic in itself
has well-marked poisonous properties, but when brought in contact with
dialyzed iron it forms an insoluble compound and becomes innocuous.
Idiosyncrasies are not so noticeable in cattle practice as in practice
among human beings, but the uncertainty with which some drugs exert their
influence would lead us to believe that well-marked differences in
susceptibility exist. Even in some cases a tolerance for poison is
engendered, so that in a herd of animals equally exposed injurious or fatal
effects do not appear with uniformity. For example, among cattle that are
compelled to drink water holding in solution a salt of lead the effects of
the poisoning will be found varying all the way from fatality to
imperceptibility.

GENERAL SYMPTOMS OF POISONING.

It is not always easy to differentiate between poisoning and some disease.
Indeed, examination during the life of the animal is sometimes wholly
inadequate to the formation of an opinion as to whether the case is one of
poisoning or, if it is, as to what the poison may be. A chemical and
physical examination aft