CHAPTER XXVIII 

 AIR AND LIFE 



172. Energesis. The activity of protoplasm is made possible 

 by a chemical process that sets free heat, or light, or motion, 

 or some other form of energy. In this process oxygen is 

 usually concerned, and it may be called energesis, or " energy 

 making." 



173. Life without air. In the yeast and in certain other 

 simple plants there are ferments that bring about the break- 

 ing down of carbohydrates into simpler compounds, as alcohol 

 and carbon dioxid, in the absence of oxygen. Such organisms 

 are called anaerobic ; that is, " living without air." The carbon 

 dioxid given off by anaerobes, although not the direct result of 

 oxidation, is still a by-product of energesis.^ 



The German physiologist Pfliiger placed a live frog in a 

 vacuum and found that the animal continued to give off carbon 

 dioxid. This showed that the carbon dioxid given off by a 

 living organism is not directly related to the oxygen taken in. 

 And this has been shown over and over again by means of 

 careful experiments, in which the gas exchange was accurately 

 measured. 



174. Oxygen in energesis. But if the oxygen does not 

 combine with the carbon and hydrogen of the protoplasm 

 compounds, what has it to do with the chemical processes 

 in a living cell } It seems that the chemical changes can 

 take place only in the presence of water, and that under the 



^ We can perhaps form a picture of anaerobic energesis by comparing the 

 chemical process to what happens when a pile of blocks is caused to break 

 down by the removal of one or two of the supporting blocks. As the structure 

 falls down into simpler combinations, a great deal of energy may be set free. 



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