Some peculiarities of australian snake venoms

Abstract

The Australian colubrid snakes present a gradual transition in morphological characters towards the viperine type. There is no similar regular transition in the venoms, though these exhibit certain points of difference from the venoms of other colubrid snakes. Viperine venoms are not so toxic as those of the colubridæ. They possess powerful thrombins, but usually kill by causing peripheral circulatory failure, which is contributed to by cytolysis of vascular endothelium. They are weak in hæmolytic and curari-like action. The venoms of the colubridæ generally possess no thrombins, but contain powerful hæmolysins and are predominantly curari-like poisons. Some have an additional direct action on muscle. They cause death by paralysis of respiration, but this is a peripheral and not a central action. Some of the Australian venoms are powerfully coagulant. Hæmorrhagins are not strongly represented. Their hæmolysins, though generally similar in action to those of other colubrid venoms, exhibit certain points of difference. They are not influenced by the presence of complement. Serum frequently inhibits instead of activating hæmolysis. The hæmolysins, though they cause inhibition of hæmolysis when present in excess, do not render the cells less susceptible to other lytic agents. The Australian venoms are peculiarly toxic when administered subcutaneously and though this is in part due to their curari-like action it cannot so be wholly accounted for. There is no convincing evidence of direct action on the central nervous system and their extreme toxicity may be due also in part to action on the peripheral circulation. On smooth muscle the Australian venoms exhibit a wholly peculiar action, which resembles the anaphylactic response of sensitive plain muscle. Similar effects can be demonstrated upon the isolated uterine muscle and upon the intact vascular system. The potency of this action on smooth muscle is closely paralleled by the lethal action of the venoms when injected subcutaneously in laboratory animals.