RESPIRATION OF THE TISSUES 



blood comes in contact with the surface of the tubes and 

 absorbs oxygen from the air in them. As they possess no 

 hemoglobin or red blood cells, oxygen is simply dissolved 

 in the blood ; but owing to the small size of their bodies, 

 this is sufficient for their use. 



374. Respiration in shellfish. Shellfish, such as oysters 

 and clams, have gills like fringes along their front edges. 

 The gills are covered with cilia which cause currents of 

 water bearing food and air to flow through the shell. 



375. Respiration in plants. A plant also breathes. 

 While it uses heat from the sun in the manufacture of 

 starch from the carbonic acid gas and water, yet for its 

 own movements it requires a production of heat within 

 itself. In order to climb a pole and unfold its flowers, a 

 vine requires power which is furnished by the oxidation of 

 its own substance. At the height of the flowering season 

 the temperature of the plant is raised slightly above that 

 of the surrounding atmosphere, and carbonic acid gas is 

 given off. In every case the heat and power is furnished 

 by oxidation of some of the plant's own substance, but the 

 amount of carbonic acid gas given off is insignificant in 

 comparison with the amount of carbonic acid gas which 

 the plant uses as food. A little oxygen is absorbed by 

 the leaves, but it is small in amount compared with what 

 is given off by the plant. 



SUMMARY 



1. As blood passes through the capillaries of the lungs it 



gives carbonic acid gas to the air and takes about 

 the same amount of oxygen from the air. 



2. As blood passes through the capillaries of the body it 



gives up oxygen to the cells and takes carbonic acid 

 gas from the cells. 



