Amphibians have several unique and clinically relevant
anatomical characteristics. The first is they go through
metamorphosis and change from strictly aquatic larval
(i.e., tadpoles) to terrestrial adults. These metamorphoses
include dramatic anatomical changes; growth of
legs, loss of gills, and formation of lungs. As a completely
aquatic tadpole with gills, they have a very similar respiration
to fish. As adults with lungs, they can leave their
aquatic environment and respire out of water. For these
reasons it is impossible to drown a tadpole, but an anesthetized
toad immersed in water can aspirate through its
nose and drown. The unique semipermeable amphibian
skin allows anesthetic drugs and oxygen to cross. This is
very useful for application of anesthetic drugs topically
with systemic effects. It also allows animals to respire
and maintain appropriate blood oxygen levels without
pulmonary respiration (Stetter, 2001; Wright and
Whitaker 2001; Crawshaw, 2003).