Permit me to state at the outset that such information as may be contained in this chapter is not the result of conjecture and guesswork, but is derived from over twenty-five years study of reptilian zoölogy, many years investigation in the laboratory, during which time an extended series of experiments were carried out, and twelve years' actual practice, in which all of the methods that have suggested from time to time have been thoroughly tested. There are, roughly speaking, something like twenty-eight varieties of venomous reptiles in the United States. These figures include the one lizard that is known to be poisonous and the several scorpions. Of this number the rattlesnakes comprise at least eighteen. In fact, so important are they that all others may be included in a discussion of the crotalidæ; more particularly so as all serpent venoms act chemically in the same manner. Man is unreasoningly afraid of snakes. It is rare, indeed, that a person concerns himself with the classification of the serpent that chances to cross his path. He immediately possesses himself of a stout club and proceeds to maul the unoffending reptile into the earth without troubling his mind to find out if the snake is harmless or otherwise. This is wrong, for when one comes to know them serpents are quite interesting. It is wrong, too, for with a little study the ordinary man can familiarize himself with the characteristic markings of the venomous serpents and differentiate them from those that are non-venomous. All the deadly snakes, with the exception of the little harlequin snake of the extreme South, are similarly marked and all belong to the class of "pit" vipers, characterized by a depression or "pit" back of the nostril. The head is triangular, with massive muscular development of the jaw; the neck slender in proportion to the size of the head and body. The body itself is quite thick, the skin rough. The pupil of the eye is elliptical instead of being round as in the non-venomous snakes. The harmless varieties, on the other hand, are long and slender, the skin smooth and shining, the head oval or round. If in doubt after the above, the investigator can pin his subject to the ground with a forked stick placed just back of the head and examine the teeth. If he finds, hanging from the upper jaw, or inclined forward from it, two fangs, long and sharp as needles, he can be pretty safe in assuming that his subject is poisonous. The non-venomous snakes have a dentition very much the same as some of the smaller rodents, the mice for instance. The habitat frequently furnishes a key to the character of the snake. The venomous varieties choose by preference the rocky uplands, either open or sparsely wooded. The harmless snakes live almost exclusively in low swampy lands or along water courses. Venomous snakes are purely terrestrial. One was never known to ascend a tree. In fact it is impossible for one to do so.