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of the arc lamp. Among other sources of energy is that of chemi- 

 cal combination. A chemical compound in the production of 

 which energy has been used is simply a storehouse of that energy 

 and can under proper conditions be made to give it up again ; 

 the giving up resulting in decomposition whether it be a simple 

 compound or a complex group as in the tissues of living animls. 

 In attempting to make this clear allow me to draw a parallel. The 

 heat of the sun is one source of energy. This heat causes the sur- 

 face water of the ocean surrounding us to be continually vapor- 

 ized. This water vapor, when the upper strata of the atmosphere 

 can hold no more, is precipitated as rain. Some of this rain falls 

 in Nuuanu Valley and finds its way into the reservoirs. The water 

 in these reservoirs is in virtue of its position, several hundred feet 

 above sea level, capable of doing work ; in fact does work or is 

 made to generate electricity and light our streets. The stored 

 water represents simply some of the sun's energy and today we 

 need no Joshua to command the sun to stand still for we can bot- 

 tle up the sun's energy by day and have it on tap by night when 

 and where we please. 



Sunlight is another source of energy. Growing plants by a 

 complex and little understood process make use of this energy 

 and build up by it out of the carbonic acid of the air and simple 

 nitrogenous compounds obtained from the soil the complex or- 

 ganic compounds characteristic of plants. Practically all the 

 essential parts of plants represent stored up sunlight just as reser- 

 voir water represents stored up sun heat; and just as stored up 

 water can be made to do work by letting it flow to a lower level 

 so the complex compounds of plants can be made to do work by 

 letting them down so to speak to a lower level, decomposing them 

 into simpler forms. Foods then are such higher level compounds, 

 and every act or motion of living animals is simply the setting 

 free of energy, which at some time has been stored up by plant 

 from that given out by the sun. Of course all plant products 

 are not food. Some are not digestible, such as woody fibre, the 

 energy of which can be set free by burning. Others are simpl? 

 compounds which have been already reduced to a lower level dur- 

 ing the growth of the plant. 



Chemically food material has been divided into three general 

 groups: I. Protein, the nitrogenous compounds. II. Carbo- 

 hydrates comprising sugars and starches, and III. Fats. For 



