268 
CROCODILES AND SNAKES 
equally true of every member of the group. But there are, neverthe¬ 
less, certain rules with regard to these animals to which there is no 
exception. They are all, for instance, what we call “cold-blooded 
that is, their blood is not so thoroughly mingled with air in its passage 
through the lungs as is that of the mammals and the birds. Much of it, 
indeed, passes through the body more than once without entering the 
lungs at all, the heart sending only a part to be purified, and allowing 
the remainder to circulate as before without being freshened by contact 
with the air. And as the heat of the body depends almost entirely upon 
the manner in which the blood is purified, the faster it travels through 
the body, and the more often it passes through the lungs, the greater 
becomes the bodily warmth. 
The heart and other blood vessels of the reptiles are formed in a 
different manner from our own, and the blood flows through them 
quite slowly, so that it never becomes very warm, and causes the body 
to feel quite cold to the touch. And, in consequence, nearly all reptiles 
are dull and sluggish in their movements, unless they are aroused by 
passion. 
No reptile of any kind is provided with either fur or feathers; 
and the reason of this is evident enough, for, as its blood is cold, 
there is no need for the body to be clothed in the warm garments 
which are so necessary to mammals and birds. Some protection, how¬ 
ever, the body must have, and so it is covered with either plates or 
scales, according to the character of the life which it is intended to lead. 
The now existing reptiles are divided into four orders. These are 
the crocodiles, the tortoises or turtles, the lizards and the snakes. To 
these we have here, for the sake of convenience, added the frogs, 
although these are now properly considered as a family by themselves, 
differing from the reptiles in several important ways. 
The crocodiles and alligators are the very lions and tigers 
of the reptile world. The animals pass much of their time in the 
water, and are never found very far from the rivers in which they 
dwell. Upon dry land they are slow, awkward, and even clumsy 
creatures, for their short limbs are scarcely strong enough to support 
their bodies, and they waddle along in consequence, very much as do 
the over-fed lap-dogs which we sometimes see in the streets. But in 
