278 
RESPIRATION OF REPTILES AND BIRDS. 
of Frogs is of great importance in their respiration—in fact, 
of almost as much consequence as their lungs. The necessity 
for more energetic respiration increases in these animals with 
the temperature, every rise in which excites them to greater 
activity. During the winter, which they pass beneath the 
water in a state of torpidity, the action of the water upon 
their skin is sufficient to aerate their blood. When the re¬ 
turning warmth of spring arouses them from their inaction, 
they need a larger amount of respiration, and come occa¬ 
sionally to the surface to take-in air by their lungs. And 
when summer comes on, the greater heat increases their need 
of respiration; and they quit their ditches and ponds, so as 
to allow the atmosphere to act upon their skin as well as 
upon their lungs. If they are prevented from doing so, they 
will die; and the same result follows if the skin be smeared 
with grease, so that the air cannot permeate it. Moreover, if 
the lungs be removed, and the animal be made to breathe by 
its skin alone, it may live for some time, if the temperature 
be not high. These facts show the great importance of the 
skin as a respiratory organ in Frogs. 
326. The respiration of Birds is more active than that of 
any other Yertebrata; that is, they consume more oxygen, 
and form more carbonic acid, in proportion to their size. 
