THE LIBERATION OF ENERGY 57 



bottle E is a trap for any carbon dioxide produced 

 by the plant which has managed to pass bottle D. 

 Bottle E is in connection with a pump or aspirator, 

 by which air can be sucked through the whole appara- 

 tus. (Care must be taken that all joints are made 

 absolutely air-tight and that the bell-jar is vaselined 

 to a glass plate.) If the pump be started it will be 

 found that bottle B becomes milky owing to the 

 presence of carbon dioxide in normal air, but so long 

 as C remains clear, we may be sure that the plant in 

 A is receiving nitrogen and oxygen only. Since 

 oxygen is being supplied, respiration is possible. 

 Very soon bottle D, next the glass bell- jar on the 

 other side, also becomes milky from the formation 

 of calcium carbonate the carbon dioxide being 

 produced by respiration in the living plant. The same 

 experiment may be performed with a frog or other 

 small animal, which will live under the bell- jar, A, with- 

 out suffering any injury or inconvenience, beyond 

 imprisonment. Under these circumstances the 

 bottle D will be found to become milky much more 

 rapidly than when a plant is placed beneath the 

 bell-jar, for respiration in an animal is, under ordi- 

 nary conditions, much more vigorous than in the 

 plant. It is, of course, immaterial in this case whether 

 the bell- jar be darkened or not, since the animal has 

 no photosynthetic power. 



In addition to carbon dioxide, water and solid waste 

 materials of various kinds are produced as the result Excretion 

 of decomposition processes. Water as a waste 

 product is got rid of as water vapour along with the 

 transpiration water (p. 46) by the stomata in the case 

 of the plant, and by glandular organs, such as sweat 

 glands and kidneys in the case of animals. The 

 solid waste substances, some of which are by no 



