Although all the venomous snakes produce morbid symptoms nearly similar, yet the strength of the poison varies according to the species of the serpent, and to the circumstances under which it is emitted. It is said to be most virulent during very hot weather, when the moon changes, or when the animal is about to cast its skin. The effects are naturally more powerful and rapid when a larger quantity of poison flows into the wound, and a snake with exhausted supplies from repeated bitings will evidently strike less fatally than another whose glands are inflated with poison after a long repose. Before describing some of the most conspicuous of the venomous serpents, a few words on the simple but admirable mechanism of their delicate but needle-like fangs will not be out of place. Towards the point of the fang, which is invariably situated in the upper jaw, there is a little oblong aperture on the convex side of it, and through this there is a communication down the fang to the root, at which lies a little bag containing the poison. Thus, when the point of the fang is pressed, the root of the fang also presses against the bag and sends up a portion of the poison it contains. The fangs being extremely movable, can be voluntarily depressed or elevated; and as from their brittleness they are very liable to break, Nature, to provide for a loss that would be fatal, has added behind each of them smaller or subsidiary fangs ready to take their place in case of accident. Unrivalled in the display of every lovely colour of the rainbow, and unmatched in the effects of his deadly poison, the bush-master or counacutchi (_Lachesis rhombeata_) glides on, sole monarch of the forests of Guiana or Brazil, as both man and beast fly before him. In size he surpasses most other venomous species, as he sometimes grows to the length of fourteen feet. Generally concealed among the fallen leaves of the forest, he lives on small birds, reptiles, and mammalians, whom he is able to pursue with surprising activity. Thus, Schomburgk once saw an opossum rushing through the forest, and closely followed by an enormous bush-master. Frightened to death and utterly exhausted, the panting animal ascended the stump of an old tree, and thence, as if rooted to the spot, looked with staring eyes on its enemy, who, rolled in a spiral coil, from which his head rose higher and higher, slowly and leisurely, as if conscious that his prey could not possibly escape him, prepared for his deadly spring. This time, however, the bush-master was mistaken, for a shot from Schomburgk’s rifle laid him writhing in the dust, while the opossum, saved by a miracle, ran off as fast as he could. Fortunately for the planter and negroes, the bush-master is a rare serpent, frequenting only the deepest shades of the thicket, where in the day-time he generally lies coiled upon the ground.