CHAPTER III 

 LIBERATION OF ENERGY 



(1) CALORIMETRY 



" From the use of materials arise physical results, such as work, heat and 

 electricity, which we can express in heat units. This is the power derived from 

 metabolism." VOIT. 



THE next matter for consideration is the method of measuring 

 the potential energy of foodstuffs and comparing the value so 

 found with the actual amount of energy liberated in the organism. 

 It should then be apparent whether living matter in its various 

 energy-changes obeys the laws of energetics. For purposes of 

 measurement, it is customary in biology to convert all forms of 

 energy into that of heat. This is scientifically correct, as heat is 

 the " lowest grade " of energy, and all other forms of energy 

 (ordered motion) may be degraded to unordered motion (heat) ; 

 and it is not possible completely to convert any form of energy 

 into any other form of energy but heat. In any such conversion, 

 as we have seen, there is always a certain loss as heat. The 

 unit of heat adopted in biology is the large calorie that is, 

 1000 times the amount of heat required to raise one gram of 

 pure water from 15 to 16 C. This value is almost the same as 

 that required to raise one kilogram of water 1 C. 



Just as a country must have a standard coin of the realm 

 pound or dollar in which its assets may be computed, so must 

 there be a standard unit for the computation of energy. The 

 bank-teller totals up his day's transactions in s. d., no matter 

 how various are the forms in which he has received or parted with 

 the money. Cash, notes, cheques, deposit receipts, etc., all 

 appear on his final balance-sheet under one denomination. Simi- 

 larly, all energy transactions can be summed up and balanced 

 as so many calories received, so many calories expended. Further, 

 the fact that not a single sovereign may have crossed the counter 



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