e differences and resemblances connoting such groups of things
as fishes, birds, and furry beasts. This conception, to be sure, is an
abstraction of a relatively high order. We know that there are savage
races to-day whose language contains no word for such an abstraction as
bird or tree. We are bound to believe, then, that there were long ages
of human progress during which the highest man had attained no such
stage of abstraction; but, on the other hand, it is equally little in
question that this degree of mental development had been attained long
before the opening of our historical period. The primeval man, then,
whose scientific knowledge we are attempting to predicate, had become,
through his conception of fishes, birds, and hairy animals as separate
classes, a scientific zoologist of relatively high attainments.

In the practical field of medical knowledge, a certain stage of
development must have been reached at a very early day. Even animals
pick and choose among the vegetables about them, and at times seek out
certain herbs quite different from their ordinary food, practising a
sort of instinctive therapeutics. The cat's fondness for catnip is
a case in point. The most primitive man, then, must have inherited a
racial or instinctive knowledge of the medicinal effects of certain
herbs; in particular he must have had such elementary knowledge of
toxicology as would enable him to avoid eating certain poisonous
berries. Perhaps, indeed, we are placing the effect before the cause
to some extent; for, after all, the animal system possesses marvellous
powers of adaption, and there is perhaps hardly any poisonous vegetable
which man might not have learned to eat without deleterious effect,
provided the experiment were made gradually. To a certain extent, then,
the observed poisonous effects of numerous plants upon the human system
are to be explained by the fact that our ancestors have avoided this
particular vegetable. Certain fruits and berries might have come to have
been a part of man's diet, had they grown in the regions he inhabited
at an early day, which now are poisonous to his system. This thought,
however, carries us too far afield. For practical purposes, it suffices
that certain roots, leaves, and fruits possess principles that are
poisonous to the human system, and that unless man had learned in some
way to avoid these, our race must have come to disaster. In point of
fact, he did learn to avoid them; and