Amphibians

AMPHIBIANS, Amphibia (from the Greek amphi- on both sides and bios-life), amphibians, a class of vertebrates with two pairs of walking legs, which in some cases may be atrophied; the skull of amphibians connects to the spine by two occipital condyles (condyli occipitales). The ribs do not connect to the sternum. The heart is three-chambered (1 ventricle, 2 atria). The nasal pits are connected by choanae to the oral cavity. The urinary bladder is a protrusion of the anterior wall of the cloaca. Amphibians spawn eggs in water, and fertilization is external. Development proceeds with metamorphosis, without embryonic membranes. Larvae (tadpoles) live in water and breathe with gills. Three orders: 1) tailed amphibians (Urodela), salamanders, newts, axolotls; 2) tailless (Anura), frogs, toads; 3) legless (Apoda), caecilians. The skin of amphibians is very rich in saccular glands secreting a serous or mucous fluid. The serous secretion in all studied amphibians is poisonous. The toxicity of the poison of some amphibians is so great that it is used as an arrow poison (Dendrobates tinctorius, South America). The properties of salamander and toad poison have been studied best. Behind their eyes, they have parotids, i.e., powerful clusters of serous glands. When irritated, the poison is squeezed onto the skin surface. There are no wounding devices in the poison glands of amphibians; therefore, their poison ordinarily gets only onto the mucous membranes and integuments of humans or animals. The pharmacological effect of the poison is very great. An aqueous extract from dried toad skin (Bufo cinereus and B. viridis) when injected under the skin acts as a cardiac poison, causing the heart to stop in systole. In warm-blooded animals, cardiac arrest is followed by a violent period of asphyxiation. The poison acts on the motor nerve ganglia of the heart and on its muscle tissue. On the circulatory organs, toad poison acts similarly to digitalis glycosides. It possesses local anesthetic properties, which enabled Staderini to perform various eye operations by introducing an aqueous solution of toad poison into the eye. In folk medicine, for the treatment of toothache, a live toad is applied to the gums. Cases of death are known from such treatment due to poisoning by the poison absorbed by the mucous membrane of the gums (Argentina).