CHAPTER V 
MEDICINAL AND POISONOUS PLANTS 
59. Medicines and poisons. It is an old saying that 
medicines are substances which make the sick well and the 
well sick. This saying expresses in a way the truth that 
among medicines are included some of the most powerful 
poisons known. In fact, most medicines are poisonous, and 
most poisons medicinal. Experience has shown also that 
when a fatal dose of a certain poison has been taken, life 
may sometimes be saved by giving, as an antidote, some other 
poison in quantity sufficient even to cause death if the first 
poison had not already been taken. | 
From these facts it appears that no line of separation can 
be drawn between medicines and poisons. By a medicine 
we mean any substance used for the cure or relief of disease; 
and by a poison, any substance capable of injuring the body 
by other than mechanical means so as to cause death or 
serious harm if taken in undue quantity. Even too much 
food may be harmful or perhaps fatal, and the same is true 
of the most harmless medicines, but in these cases the bad 
effect is so largely the mechanical result of excessive quantity 
that we do not say poisoning has taken place. Foods are 
sometimes used as medicines, as, for example, olive-oil and 
Irish moss. The same is true of food-adjuncts in general, 
and, as we have already seen, many of these if taken in more 
than small amount are poisonous. We may recall also the 
fact that certain foods, such as tapioca, are obtained from 
plants which contain deadly poisons. Similarly the tubers 
of the white potato when young or when green in color, 
contain a powerful poison. Thus it is plain, that edible, 
medicinal, and poisonous plants must not be thought of as 
entirely separate and distinct classes, but merely as groups 
made for practical convenience. 
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