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real process, to which the physiologist applies the term respira- 

 tion, has to do with the use that is made of the inspired air. 

 From the lungs this air, in man for example, is taken up by the 

 blood. Part of it the blood uses in its own respiration, the re- 

 mainder it carries to all the tissues of the body, and delivers it to 

 the individual protoplasmic units or cells. These cells take up 

 the oxygen according to their needs, use it in performing 

 their work, and return to the blood the carbon dioxide that re- 

 sults. Carried by the blood back to the lungs, the carbon 

 dioxide is given off to the air in expiration. All of this is com- 



which goes on in the individual cells, while the term breathing 

 may be to advantage restricted to the work of the lungs. Res- 

 piration, then, is a cell-process, and every organism that is alive, 

 and every living cell of that organism must respire. The cells of 



of the lungs. All plants are built up of cells, some of which are 

 alive and some not. All the living cells of plants respire, just as 

 truly as do those of animals. 



It is difficult to demonstrate the cell processes, but the out- 

 ward manifestation of them — the absorption of oxygen and the 

 evolution of carbon dioxide — is very easily shown. 



Into each of six fruit jars place portions of the different parts 

 of plants as follows : into the first fresh roots, into the second 

 stems, into the third leaves, into the fourth flowers, into the fifth 

 germinating seeds, and into the sixth nothing. A lighted candle 

 will continue to burn when placed in any of the jars. Seal them 

 all air tight. If, at the end of twelve hours, a lighted candle is 

 thrust into each of the jars, it will be extinguished in each of the 

 first five, but will continue to burn as usual in the sixth. This 

 shows us that the air in the five jars has become poorer in oxy- 

 gen, while that in the sixth jar is apparently unchanged. If now 

 we pour clear lime-water into each of these jars, the water will 

 become milky in each of the first five, but will remain clear in 

 the sixth. This indicates that in the first five the amount of car- 

 bon dioxide has been increased, but not so in the sixth. 



Since the only difference between the first five jars and the 



