[10] Strickler and Goldberg, _Jour. Amer. Med. Assoc._, LXVI (1916), 249. [11] _Jour. Cutaneous Dis._, XXXIV (1916), 70. [12] _Amer. Jour. Dis. of Children_, XI (1916), 441. CHAPTER III POISONOUS PLANTS AND ANIMALS Some normal plant and animal tissues contain substances poisonous to man and are occasionally eaten by mistake for wholesome foods. POISONOUS PLANTS Poisonous plants have sometimes figured conspicuously in human affairs. Every reader of ancient history knows how Socrates "drank the hemlock," and how crafty imperial murderers were likely to substitute poisonous mushrooms for edible ones in the dishes prepared for guests who were out of favor. In our own times the eating of poisonous plants is generally an accident, and poisoning from this cause occurs chiefly among the young and the ignorant. According to Chesnut[13] there are 16,673 leaf-bearing plants included in Heller's _Catalogue of North American Plants_, and of these nearly five hundred, in one way or another, have been alleged to be poisonous. Some of these are relatively rare or for other reasons are not likely to be eaten by man or beast; others contain a poison only in some particular part, or are poisonous only at certain seasons of the year; in some the poison is not dangerous when taken by the mouth, but only when brought in contact with the skin or injected beneath the skin or into the circulation. There are great differences in individual susceptibility to some of these plant poisons. One familiar plant, the so-called poison-ivy, is not harmful for many people even when handled recklessly; it can be eaten with impunity by most domestic animals.