COMPOSITION OF LIVING THINGS 27 



Conservation of energy. Physical science teaches us that 

 energy, such as that released so disastrously in that California 

 valley, may never be lost, created, or destroyed. It always is, 

 and always has been. The great force, released when the flood 

 rushed down the valley, dug deep channels in the soil, moved huge 

 rocks, smashed houses, and left countless other ruins in its ruthless 

 path. If the water could have been harnessed to a turbine, it 

 might have turned a dynamo, produced electricity, lighted a city, 

 or turned the wheels of factories. Energy may be changed from 

 one form to another, but it can never be created or destroyed ; it 

 is everlasting ! 



Practical Exercise 2. Give three examples of transformation of energy that 

 helps to make life more comfortable for you. 



Water in living things. Water forms an important part of the 

 substance of plants and animals. This is seen when a number of 

 green leaves are weighed, placed in a hot oven for a few moments, 

 and then re weighed. The same experiment made with a soft- 

 bodied animal, as the oyster, would show the presence of a greater 

 percentage of water than was found in leaves. Some jellyfish 

 are over 90 per cent water. Over 65 per cent of the human body 

 is water. 



Mineral matter in living things. If a piece of wood is burned 

 in a very hot fire, the carbon in it will all be consumed, and even- 

 tually nothing will be left except a grayish ash. This ash consists 

 of mineral matter which the plant has taken up from the soil dis- 

 solved in water, and which has been stored in the wood or leaves. 

 All living things contain small quantities of mineral substances. 



Practical Exercise 3. Weigh several different substances such as soil, apple, 

 meat, dried beans, celery, etc. Dry out each substance in an oven under slow 

 heat (do not char) . After several hours reweigh and determine percentages of 

 water lost by each substance. Then try to burn out all organic material. 

 The gray residue is the ash or mineral content. What per cent of the orig- 

 inal weight is the ash? 



Gases present in living things. Some gases are found in a free 

 state in the bodies of plants or animals. Oxygen is of course 

 present wherever oxidation of organic matter is taking place, as is 

 carbon dioxide. Other gases may be present in minute quantities. 



