For a long time this name was given indiscriminately to all lizards of this kind, living either south or north of the boundary line of Mexico and the United States, till Professor Cope discovered a difference between them and called the variety found in our southwestern territories and states Heloderma suspectum. Many other naturalists have since taken up the study of this interesting reptile. The result of their observations and experiments was that they all agree in acknowledging the Heloderma as the only poisonous lizard in existence, although their opinions are at variance as to the effect of its venom on the human system. Dr. van Denburgh in his latest researches has found two glands, one on each side of the lower jaw, located between the skin and the bone. Such a venom-producing gland being taken out of its enveloping membrane proves to be not a single body, but an agglomeration of several small ones, differing in size, and each emptying through a separate duct. These glands are not directly communicated to the teeth. When the animal is highly irritated, caused by constant teasing or rough handling or by being trodden upon, the poison is emitted by the glands, gathers on the floor of the mouth, where it mixes with the saliva, and is transmitted through the bite. A Heloderma has no fangs, but a goodly number of sharp, pointed teeth, both on the upper and lower jaws. They are curved backward and about an eighth of an inch long, or even less than that. The principal characteristic of these teeth is that they are grooved, facilitating thus the flow of the venom into the wound. It bites with an extremely swift dash, directed sideways, and holds on tenaciously to whatever is seized with its powerful jaws. Sumichrast says when the reptile bites it throws itself on its back, but none of the later naturalists makes mention of this peculiarity. The venom of the Gila Monster injected into the veins and arteries of smaller animals as rats, cavies and rabbits and into the breast of pigeons and chickens, causes death within twenty seconds to seven minutes. Brehm relates that a young Heloderma, and in poor physical condition besides, was induced to bite the leg of a large, well-fed cat, which did not die, but gave signs of prolonged terrible sufferings. It became dull and emaciated and never regained its former good spirits. Among several cases of Gila Monster bites inflicted on human beings can be quoted that of Dr. Shufeldt, who, in “The American Naturalist,” gave an interesting account of the sensations he experienced. It is sufficient to say that the pain, starting from a wound on the right thumb, went like an electric shock through the whole body and was so severe as to cause the victim to faint. Immediate treatment prevented more serious consequences. The Doctor, nevertheless, was a very sick man for several days and began to recover only after a week had elapsed. [Illustration: ]