LAW OF THE CONSERVATION OF ENERGY 569 



"La Republique n'a pas besoin de savants" which was true, until 

 1870, let us say, or 1914. It is to a Roman politician that we owe the 

 very popular and oft-quoted doctrine that "The Voice of the people 

 is the Voice of God." On this occasion the spokesman of the people 

 assured one of the greatest discoverers that humanity has produced, 

 that a republic had no need of him or of his kind. To a Swedish 

 physicist, Oersted, we owe a different doctrine, which he expressed in 

 these words: "The Laws of Nature are the Thoughts of God." If 

 we should estimate the value of these two doctrines by their fruits, 

 then doubtless we would prefer the doctrine of the physicist who 

 produced telegraphy to that of the demagogue who planned a brutal 

 and senseless murder. Contemporary events will doubtless, in time 

 to come, furnish us with an abundance of additional means of estimat- 

 ing the relative value of these theories. 



The work which had been thus initiated by Lavoisier, was carried 

 on by his pupil Liebig, who, however, mainly devoted his attention and 

 his life's work to the firm establishment of the Law of the Conser- 

 vation of Matter in its application to living organisms. The methods 

 of organic analysis which he devised, and the investigations which he 

 undertook, laid the foundations of analytical biochemistry as we know 

 it today. The energy-transformations of life were destined to become 

 the preoccupation of Liebig's pupil, Voit, and of a series of investi- 

 gators who owed to Voit their inspiration. Thus, to the second and 

 third generations of investigators succeeding Lavoisier, fell the task 

 of achieving the fruition of his labors. 



In order to render possible an accurate comparison of the kind which 

 was attempted by Lavoisier it was first of all necessary to ascertain 

 Heats of Combustion of the various foodstuffs. The actual fuels burnt 

 by the animal machine are carbohydrates, fats and proteins, and it 

 is evidently with the heat of combustion of these substances, and not 

 merely that of carbon, tjiat we should compare the heat-evolution of 

 an animal. 



The Calorific Values in heat-units per gram for the different repre- 

 sentatives of the three main classes of foodstuffs do not vary greatly 

 among themselves. The molecules of the Fats and Proteins are 

 so large that the differences of composition or structure which they 

 display affect the total heat of combustion but slightly, while the 

 Carbohydrates uniformly contain the proportion of oxygen which is 

 requisite to burn their hydrogen and hence the combustion-value for 

 each carbohydrate is very nearly proportional to the carbon which it 

 contains and this in turn is proportional to the weight of the molecule. 

 The following are the calorific values of various foodstuffs, as esti- 

 mated by complete combustion in a calorimeter, the heat-output 

 being expressed in terms of the large calorie, or quantity of heat re- 

 quired to raise the temperature of one kilogram of water from C. 

 to 1 C. 



