RESPIRATION. 139 



very carefully tied, are no security against the impetus of 

 the blood. 



RESPIRATION. 



412. 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. 



413. 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 injects change into 

 larvae if confined in a vacuum. 



414. Even the most minute animals, and those which 

 are most tenacious of life, as the infuriosa, which may be 

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

 moistening, are still unable long to survive when deprived 

 entirely of air. 



415. 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 amply 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. 



416. As we ascend the scale of organization, we find 

 that animals require more and more air, and that they in- 

 crease 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 arethe same. In others this func- 



^^ \ 



What is meant by respiratinfc ? Whatis*said of the necessity of air to 

 plants and animals ? Where do fish obtain air ? What is the difference 

 between the lower and higher orders with respect to air * 



V 



