ORGANS OF RESPIRATION. 27i 



But this apparent opposition between the phenomena of animal and 

 vegetable life only exists because plants have the special power of pro- 

 ducing organic matter, by which they become the source of nourish- 

 ment for the entire living creation. The organic substances so pro- 

 duced do not immediately take part in the more active phenomena even 

 of vegetable life. They are, on the contrary, deposited in a more or less 

 quiescent form, and constitute a reserve material, to be afterward trans- 

 formed and assimilated by the plant, or consumed by herbivorous ani- 

 mals. In vegetables, as well as in animals, a true respiration also takes 

 place, which is marked in both instances by the absorption of oxygen. 

 The deoxidizing process, by which organic matter is produced, occurs 

 only in green vegetables, and under the influence of the solar light ; 

 while the absorption of oxygen is a constant phenomenon, taking place 

 in both green and colorless plants, and in darkness as well as in the 

 light. 



The more active phenomena of vegetation, moreover, are immediately 

 dependent upon the absorption of oxygen, and cannot go on without it. 

 When the starch which has been stored up in the seed becomes liquefied 

 and converted into sugar, and the process of germination and growth 

 begins, the absorption of oxygen is necessary to its continuance. This 

 is seen not only in germinating seeds, but also in expanding leaf and 

 flower buds, all of which organs consume in a short period several times 

 their volume of oxygen. The processes of germination, growth, and 

 flowering, as well as the intra-cellular movement of the vegetable plasma, 

 the motions of the sensitive-plant in response to stimulus, and the pe- 

 riodical movements of the leaves in certain other vegetable species, all 

 cease in an atmosphere deprived of oxygen. 1 The function of respira- 

 tion is accordingly a universal one, and essential to all forms of vital 

 activity. 



Organs of Respiration. 



The process of respiration takes place very actively in the mamma- 

 lians and birds, less so in reptiles and fishes ; and in these different 

 classes the organs by which it is accomplished vary in size and struc- 

 ture according to the activity of the function itself. Its necessary con- 

 ditions everywhere are that the circulating fluid should be exposed in 

 some way to the influence of the atmospheric air or of an aerated fluid. 

 The respiratory apparatus, accordingly, consists essentially of a moist 

 and permeable animal membrane, termed the respiratory membrane, 

 with bloodvessels on one side of it, and air or an aerated fluid on the 

 other. The blood and the air, consequently, do not come in direct con- 

 tact with each other, but absorption and exhalation take place through 

 the respiratory membrane which lies between. 



1 Mayer, Lehrbuch der Agrikultur-Chemie. Heidelberg, 1871, Band i. pp. 

 91-95. 



