FIRST GREAT DIVISION OF THE ANIMAL 

 KINGDOM. 



CLASS III. 



REPTILIA. 



The disposition of the heart in Reptiles is such^ that at each 

 contraction^ a portion only of the blood it has received from 

 the different parts of the body is transmitted to the lungs, the 

 remainder returning to those parts without having passed 

 through the pulmonary organs, and without having respired. 



The result of this is, that the action of oxygen upon the 

 blood is less than in the Mammalia, and that if the quantity of 

 respiration in the latter, in which all the blood is compelled 

 to pass through the lungs before it returns to the rest of the 

 body, be expressed by a unit, that of Reptiles will be ex- 

 pressed by a fraction of a unit, so much the smaller, as the 

 quantity of blood transmitted to the heart at each contraction 

 is less. 



As it is from respiration that the blood derives its heat, arid 

 the fibre its susceptibility of nervous irritation, the blood of 

 reptiles is cold, and the muscular energy less than that of 

 Quadrupeds, and much less than that of Birds ; thus we find 

 their movements usually confined to crawling and swimming ; 

 for, though at certain times several of them jump and run 

 with considerable activity, their habits are generally lazy, 

 their digestion excessively slow, and their sensations obtuse. 

 Vol. II.— a 



