RESPIRATION. 143 



very carefully tied, are no security against the impetus 

 of the blood. 



RESPIRATION. 



Respiration or breathing, is the act of receiving a 

 portion of air into, and throwing it out of the lungs. 

 Receiving the air, is called inspiration, and rejecting it, 

 expiration. 



Atmospheric air is so absolutely necessary to the 

 organized creation, that neither plant nor animal can 

 live without it. No vegetable seed will germinate 

 without a portion of air, nor will the eggs of insects 

 change into larvae if confined in a vacuum. 



Even the most minute animals, and those which are 

 most tenacious of life, as the infusoria, which may be 

 dried and kept any length of time, and revived again by 

 moistening, are still unable long to survive when depri- 

 ved entirely of air. 



It is true that a great proportion of animals are so 

 constructed as to require but a very minute portion of 

 air. Thus the Mollusca, and Fish, which live constantly 

 under water, can only receive that with which the fluid 

 is mixed. But the Creator has ampiy provided for the 

 wants of these creatures in this respect, by giving the 

 fluid in which they live, the power and propensity to 

 absorb air, so that water in its natural state, at whatever 

 depth from the surface it may be taken, is always found 

 to contain a portion. But if the water in which a fish 

 is confined be covered with oil, by which, the air is 

 entirely excluded, the fish soon dies. 



As we ascend in the scale of organization, we find 

 that animals require more and more air, and that they 

 increase in vivacity and power in some proportion to 

 the quantity which they consume. In the very lowest 

 orders there is no provision of any special organs for 

 respiration. Thus in some of the Zoophytes the organs 

 of nutriment and those of respiration are the same. In 



What is meant by respiration ? What is said of the necessity of air 

 to plants and animals ? Where do fish obtain air 1 What is the differ- 

 ence between the lower and higher orders with respect to air ? 



