4US PROPERTIES AND FUNCTIONS 



usually longer that they may fly with more rapidity, and 

 thereby be enabled to overtake their prey ; they have 

 strong hooked bills and long sharp claws. The grani- 

 vorous birds resemble very much the herbivorous quadru- 

 peds, both in the capaciousness of theiy stomachs and in 

 the mildness of their dispositions. It is among this class 

 of birds that man, ever attentive to his interest, has made 

 selections for the purpose of domestication. Carnivorous 

 birds never, with but one exception, herd together in 

 flocks, but they spend their time in some sequestered 

 spot, or in the depths of the forest. 



The influence of atmospheric air is absolutely neces- 

 sary for the support of organic life. This is not confined 

 to animal life : for vegetables cease to perform their 

 functions when deprived of it, and the seed will not 

 sprout unless it comes in contact with this elastic but all 

 important fluid. Plants have no particular apparatus by 

 which they respire, but they receive the air through every 

 pore. Animals are furnished with a particular apparatus 

 tor the purpose of admitting air into the internal parts 

 of the body. In man, and the most perfect animals, re- 

 spiration, or the act of breathing, is carried on by means 

 of organs called lungs, which are composed of an infi- 

 nite number of air-cells and minute blood-vessels. Re- 

 spiration consists of inspiration or the act of drawing in 

 the air into the lungs, and expiration or the act of throw- 

 ing it out. At each inspiration the little cells of the 

 lungs are filled with air. These cells are surrounded by 

 minute blood-vessels, and thus the blood which is thrown 

 from the heart and the air which enters the lungs, are 

 made to approximate each other. 



Through the influence of the air which fills the cells, 

 the blood in the minute vessels is so operated upon that 

 it is deprived of its dark color, or is changed from a dark 

 to a light red. This change takes place by the blood 

 being deprived of its impurities, which, if allowed to cir- 

 culate through the body, would not only unfit it for 

 nourishment but life would soon be destroyed. The air 

 which enters the lungs pure, returns from them loaded 

 with impurities. Changing the impure into pure blood,. 

 gr relieving it of a poisonous substance,, are not all the 



