130 



VITAL FUNCTIONS. 



385. On inspecting the plan, fig. 84, it may be remark- 

 ed that in these animals only one half of the blood is sent 

 to the lungs before it again circulates through the general 

 system. The general circulation, therefore consists of 

 one-half arterial, and one half venous blood. We shall 

 see directly that in the warm-blooded animals the cir- 

 culation is double, and that in these all the blood is sent 

 through the lungs to be aerated or exposed to the influence 

 of the atmosphere, before it is thrown into the general cir- 

 culation. It will be seen, also, that the temperature and 

 vivacity of the latter class, depend on the exposure of the 

 whole mass of blood, to the influence of the oxygen of 

 the atmosphere, as it passes the lungs. 



386. It is owing chiefly to this limited circulation that 

 amphibious animals are so remarkably distinguished from 

 others. They are not only cold-blooded, but most of them 

 are sluggish, languid arid exceedingly tenacious of life, so 

 that they will not only bear the strongest stimulants with- 

 out injury, but may have their limbs amputated with only 

 slight marks of pain. 



387. Circulation in Fishes. In fishes the organs of 

 circulation consists of four cavities, Fig. 85. 



c, d, e,f, fig. 85, with a system of 

 veins and arteries for conveying , 

 the blood to and from the heart. ( 

 Of these cavities, d is the auricle, V 

 and e, the ventricle, c and f, 

 being dilations of the principal 

 vein and artery, at their junction 

 with the heart. The heart, in 

 this system belongs exclusively 

 to the gills or branchia, which in 

 fish are the organs of respira- 

 tion. There is no aorta proceed- 

 ing from the heart which car- 

 ries the blood to all parts of the 

 system as in other animals. 

 The branchial arteries f, convey 



What kind of blood circulates through the systems of amphibious 

 animals? To what cause are the coldness and languor of these animals 

 owing ? Which is the auricle, and which the ventricle in the heart of a 

 fish* 



