CHAPTEE XIII. 



RESPIRATION. 



THE most constant and striking phenomenon presented by living 

 organisms, both animal and vegetable, is the absorption of oxygen. A 

 supply of this substance, either in the gaseous form as a constituent 

 part of the atmospheric air, or dissolved in water or other liquids, is 

 indispensably requisite for the maintenance of life and the manifestation 

 of vital phenomena. Oxygen exists diffused everywhere over the sur- 

 face of the earth, forming rather more than one-fifth part of the volume 

 of the atmosphere, and it is dissolved in greater or less abundance in 

 the water of springs, rivers, lakes, and seas. Animals and plants, ac- 

 cordingly, whether living in the air or in the water, are surrounded by 

 media in which this substance is constantly present. Even parasitic 

 organisms, inhabiting the interior of other living bodies, and the foetus 

 during the period of its intra-uterine development, though not imme- 

 diately in contact with oxygen, are supplied with nutritious fluids which 

 have themselves been exposed to its influence. The function of respi- 

 ration consists in the process by which oxygen penetrates the substance 

 of living organisms, together with the changes which accompany and 

 follow its introduction. 



Respiration in Vegetables. In regard to the phenomena of respira- 

 tion in vegetables, a distinction is to be made between respiration proper 

 and the absorption of gaseous matter for the production of organic 

 material. It is well known that all green plants, under the influence 

 of the solar light, have the power of absorbing carbonic acid and water, 

 and of partially deoxidizing these substances, to form, with their re- 

 maining elements, starch, cellulose, and fat. The oxygen thus sepa- 

 rated from its inorganic combinations is exhaled by the plant in a free 

 form ; while, as a result of the process, an accumulation of organic ma- 

 terial takes place in the vegetable fabric, which increases in substance, 

 and may afterward serve for the nutrition of animal bodies. This ac- 

 cordingly is not a process of respiration, but one of organic production. 

 It is peculiar to vegetables, animals having no power to produce organic 

 material, and therefore depending upon vegetables for their supply of food. 



Animals, on the other hand, consume the organic material thus pro- 

 duced, at the same time absorbing oxygen and exhaling carbonic acid 

 and water. In this respect there is an opposition between the actions 

 of animal and vegetable life, by which they stand in a complementary 

 relation to each other. Vegetables produce organic matter by a process 

 of deoxidation ; animals consume it with the phenomena of oxidation. 

 (270) 



